Drop flat-ui

There is nothing flat in our current theme. Just drop to flat-ui
bootstrap theme and fix the few styles we actually use from it.
Use bourbon to get rid of vendor prefixes
Balance top menu button paddings
Add placeholder for comment form
Drop extra .box-shadow class
Line up buttons for mobile too
Move TicketView spinner to right
Remove col-md-6 from top buttons

It shadowed the profile menu button from time to time