Refactor UsersController#create

* Simplify controller action
* Extract service classes
:scissors: scoped for Rails 4 compat
FIX: allow new user to post emojis
that fix should have been in the emoji plugin
FIX: images should also be inlined in the cooked view
FIX: absolute canonical link on topic pages
add image dimensions & size in lightbox
Experimental: Disqus XML importer
Merge pull request #1731 from chancancode/no_more_scoped_in_rails_4_1

:scissors: scoped for Rails 4 compat
Show more than one topic per category on the wide categories page. Disable support for the 2-column categories page. The category_featured_topics site setting controls how many topics to show.
FIX: layout problems on categories page
FIX: broken font-awesome icons on user activity pages
FIX: font-awesome issue on site settings buttons
Support for importing Disqus posts into a category
Fix category ordering on categories page. I broke it.
Updated French translation and fixed the fr_FR: to fr:
Move columns around on wide categories page
Merge pull request #1733 from voisintotoro/newmaster2

Updated French translation and fixed the fr_FR: to fr:
make sure extension-based oneboxes are first to run
Got rid of buggy yepnope spaghetti, however mobile detection really should be driven from the server.