Remove docs relating to filtering before export

[Ed McDonagh]

No longer necessary after changes introduced in #48 and #49.

[Ed McDonagh]

Fixes #48 and #49. Patient age filtering and exporting now works. Exports are now more robust rendering the modifications made for refs #28 and #43 unnecessary. Filtering before exporting is now unnecessary - see #50 for docs changes required.

→ <<cset bf88368dd533>>

[Ed McDonagh]

Removed statement about export not working until filter is applied. Refs #50.

→ <<cset 225b205fd3ea>>

[Ed McDonagh]

Templates modifed to not insist on filtering and to refer to studies rather than exams. Fixes #50.

→ <<cset 39165f2af19f>>