Make the composer and TopicCreator use category id instead of category name

Also fixes #1171
Added backwards compatibility for topic creation
Use Discourse.Resolver to load mobile templates when they exist
Detect whether to use mobile view. Session var mobile_view can override automatic detection.
Create a mobile css manifest
Store mobile flag in Discourse.Session instead of Discourse
Restructure the app/assets/stylesheets directory
rename application.css.erb to desktop.css.erb
Add link in hamburger menu to switch between mobile and desktop views
FIX: Index out of range error

Fixes 'index out of range error' that occurs when viewing a user's
profile page when they haven't yet posted a reply or created a topic
and is @mentioned in a topic.
Add span.btn-text around 'Reply' text in the post menu
Restructure login form for mobile
If mobile view, don't switch to small logo in the header when scrolled down in a topic
fix user_controller_spec when testing too long usernames
fix user_controller_spec when testing too long usernames
fix conflict
new mobile styles, some structure changes
Merge pull request #1412 from eparreno/bug/fix_users_controller_spec

fix user_controller_spec when testing too long usernames
Hide flag modal while flag is submitted
adding missing files back in