Renamed pageurl tags to wagtailcore_tags
renamed rich_text tags to wagtailrichtext_tags
Merged richtext tags into wagtailcore_tags
Moved embed_filters to wagtailembeds_tags
Moved image_tags to wagtailimages_tags
Update docs to import tags from correct tags module
Added versionchanged notes to docs
Updated deprecation warning messages of moved template tags libraries
Merge branch 'master' into feature/template-tags-rationalisation

Conflicts:
	docs/building_your_site/frontenddevelopers.rst
	wagtail/wagtailimages/templatetags/image_tags.py
Add unit tests for rich_text.py
Merge branch 'master' into rich-text-unit-tests
Alter comment formatting in wagtailcore tests.py
Merge branch 'master' into rich-text-unit-tests
Add unit tests for embed filters
Merge branch 'master' into even-more-unit-tests
Add more embeds tests
Merge branch 'master' into even-more-unit-tests
Add image format tests
Simplified UserPagePermissionsProxy.editable_pages method
Return new revision object from Page.save_revision