Collections: Add an action to put offline a collection

On the view page of a collection, add an action in the drop down list of available actions to put it available offline, like an “on/off” button.

Only the first level above "My Collections" , "Shared Collections" or "My Favorites" will be synchronised, which means:

• If a collection contains non folderish documents: they will be all synchronised
• If a collection contains folderish documents: they will not be synchronised
• Previews are also synchronised

Important: synchronising a collection means to synchronise all the documents (can abort if there is a sync interruption, detailed in the NXMOB-169).

Make it available by sliding.