Make OpenSkin integration optional

[Ed McDonagh]

Add an option as to whether OpenSkin display is available.

Also add an option as to whether maps are automatically generated with a Celery task on import, or if they are only generated on page view.

[Ed McDonagh]

Related to ab439fd and cfae5bd

[David Platten]

Made submission of skin dose settings form stay on the same page on submit. References issue #61 and issue #382

→ <<cset da1bd457582f>>

[David Platten]

Updated skin dose settings view so that the single database row is created if it doesn't exist. References issue #61 and references issue #382

→ <<cset a05b37516e9e>>

[David Platten]

Updated skin dose settings view so that the single database row is created if it doesn't exist. References issue #382

→ <<cset dc3448d62238>>

[David Platten]

Added openSkin data export back to the rfdetail page if skin dose map display is switched off. Also included the text about only Cu filters being included. Added some text to let the user know that this version of OpenREM can calculate and display skin dose maps for some systems. References issue #61, issue #382 and issue #384.

→ <<cset 128002420c9c>>

[David Platten]

I think this is complete now