Use custom user model in tests
Merge branch 'master' into test-with-custom-user-model

Conflicts:
	wagtail/tests/models.py
	wagtail/tests/utils.py
	wagtail/wagtailcore/tests/test_page_permissions.py
	wagtail/wagtaildocs/tests.py
Pull all test database options from env variables

Just pulling two and assuming others broke the base configuration I was
using, which uses a different database name and has a password.
Moved docs/images to docs/_static/images
Moved 'for django developers' to new 'Pages' section
Moved a few documents into pages section
Restructuring pages section
Moved 'for frontend developers' into Pages section
Removed contents from pages index
Moved editing_api into pages docs
Bumped south version to 1.0.0
Renamed migrations directories to south_migrations
Updated django-taggit
Added deprecation warning classes
Replaced all DeprecationWarnngs with RemovedInWagtail06Warnings
tweaks to listing styles
explorer->explore
font size minor adjustments
listing arrows always highlighted on hover now
styled editors picks help appropriately