DAR-741 Disabling the possibility to add wiki without image to a collection

Added status to the response from controller when a request is made
to add a wiki to a collection.
Added processing of that message on the client side to reflect
the actual status of the adding operation
DAR-741 UI consistency fixes

Replaced alerts with modals
DAR-741 spacing issues
DAR-741 Mediawiki cc reformatting
Merge pull request #1010 from Wikia/DAR-741

DAR-741 Disabling the possibility to add wiki without image to a collection