Update use of django-filter to work with version 2

[Ed McDonagh]

Refs #436, #17

Version pegged betwen 0.10 and 0.14 for now. Move to current version alongside Python 3, Django 2.2 etc

[Ed McDonagh]

Updated description and release milestone.

[Ed McDonagh]

Filter views now display, f.queryset instead of f in paginator, but filter doesn't display. MethodFilter replaced with CharFilter(method=. Refs #404, #437 [skip ci] not ready for tests

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[Ed McDonagh]

Basic working implementation of the DX filter. Refs #404, #437 [skip ci] not ready for tests

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[Ed McDonagh]

Starting to reinstate and update DXSummaryListFilter. Age gt not currently working. Might continue upgrade to later Django and version 2 of django_filter before attempting to fix. Refs #404, #437 [skip ci] not ready for tests

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[Ed McDonagh]

Global replace of lookup_type with lookup_expr to ease updating filters. Refs #437, #404 [skip ci] not ready for testing

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[Ed McDonagh]

Minor change to template to get number of studies. Refs #437, #404 [skip ci] not ready for testing

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[Ed McDonagh]

DX summary filtered page now working with all filters except age with django_filters 1.1, Python 3.6, Django 1.8. Need to repeat for other modalities, then move onto Django 1.9 I think. Refs #437, #404 [skip ci] not ready for testing

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[Ed McDonagh]

Starting to fix up the CT filters. Refs #404, #437 [skip ci] not for testing yet

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[Ed McDonagh]

Overcome lookup error by being more explicit; DX now has age, same for CT plus one DLP. Refs #437

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[Ed McDonagh]

Added all the other CT filters, all nominally working. Haven't looked at the order_by stuff. Refs #437

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[Ed McDonagh]

RF working as per CT, DX. Refs #437 [skip ci] - not ready for testing

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[Ed McDonagh]

MG working as per CT, DX, RF. Refs #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Name of filter has changed, test needs to change. Refs #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Starting to get the ordering filters working. Required for tests to pass!. Refs #437 [skip ci] - not ready for testing

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[Ed McDonagh]

CT Ordering in place, but without date+time modification. Prob need https://django-filter.readthedocs.io/en/1.1.0/ref/filters.html#adding-custom-filter-choices. Also no default yet. Refs #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Changed back to 'o' from 'ordering'. Added "o": "-study_date" to each of the ct export filters. Refs #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Fixed mistake in mod_filters for CT, updated tests with new filter names. Refs #404, #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Fixing display_name filtered links from homepage, code_meaning changes to rfdetail. Refs #404, #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Corrected filter arg, switched from reverse_lazy to reverse due to https://code.djangoproject.com/ticket/18776. Refs #404, #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Not sure why some mam image values are bytes that need decoding before casting to Decimal, others are float or int. Hence try:except:. Also corrected mod_filters test and reverse_lazy. refs #404, #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Change to reflect rounding of filter thickness. Second test currently failing. refs #404, #437 [skip ci] - not ready for testing

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[Ed McDonagh]

Fixing filter name and another reverse/lazy. Refs #404, #437 [skip ci] docs only.

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[Ed McDonagh]

Migrated django-filter to version 2 now we have Django 1.11. Refs #437, #457

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[Ed McDonagh]

Added ordering filters approx as before. Needs time/date modification, needs default ordering. Refs #437

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[Ed McDonagh]

Default ordering now time and date from newest; order_by choices now use time and date too. Refs #457, #437

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[Ed McDonagh]

Adding doc strings to make Codacy happy. Refs #437

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[Ed McDonagh]

Merged in p3django2.2 (pull request #337)

Update develop to Python 3, Django 2.2

Refs #530, fixes #404, #437, #457, #777

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[Ed McDonagh]

Adding changes that should have been made in pull request #337 / commit 1fc70f2. Refs #404, #437, #457, #777. Also ref #787 added to CHANGES. [skip ci] docs only

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