Upgrading to Bootstrap 3

This means for now I'm disabling support for themes!
Changed navigation menu back to a dropdown list
Added the ability to reply to messages
Highlight new messages
Made a few more minor styling updates
Added some Markdown help
Made nav menu a bit sleeker
Cleaned up a bit of CSS cruft
Added 'Member since' column to users view
Removing close button from alerts (they self-close)
Upgraded to Rails 4.0.0 final
Center that blockquote
Updated styling for comments and buttons and stuff