separate basic gallery functionality

to be more flexible with creating galleries we can separate gallery
functionality so it can be reused if developer wants to create a
gallery but not necessarily a gallery page
Fix Gallery MRO.
Added Robert Zywucki to AUTHORS.
Fixed dynamic admin inlines for subclasses doing fields magic
(assuming that InlineAdmin.fields is a user-provided list).
Added a test for DynamicInlineAdmin.
Travis test the latest versions of Django

This way you don't have to update every time a security release comes
out.
Re-instate conf test as per recent threading fixes. Closes #858.
Merge
Return HTTP 405 on comment/rating URLs for GET requests. Closes #1159.
Allow DynamicInlineAdmin fields to be a tuple.

Previously, if fields was defined as a tuple, a very confusing TypeError
would be raised.
Fix Travis Django installation
Shamelessly modified the dynamic admin fields tuple test, so it checks
get_fieldsets() instead of directly using the fields attribute.

Also made BaseDynamicInlineAdmin work when fields are listed without
the _order field or fieldsets are declared (with or without it).
SiteRelated changed to allow explicit site assignment on creation
Merge
pep8 fix
Use translated strings in relevant settings examples in project template.
Merge
Merge
Added Kelvin Wong to AUTHORS.
Fix a typo on the Content Architecture page