Created Rdoc comments for all classes and modules.

From now on any new classes/modules/methods will have their corresponding documentation.
Included Bootstrap responsive styles.
Style flash messages with Bootstrap in application layout. Moved bootstrap javascript include to AFTER including jquery, otherwise bootstrap javascript doesn't work (for instance closing alerts).
Started internationalizing Devise views.
Merge branch 'pretty-devise' of github.com:amatriain/openreader into pretty-devise