Use recipient display names when updating shares in the UI

Since OC.Share didn't have any array containing the list of shares for
the current file, OC.Share.currentShares has been introduced to contain
the full share item structure instead of the reduced one
OC.Share.itemShares.

The event "sharesChanged" is now passing OC.Share.currentShares, which
itself includes the display name to be displayed for the recipients in
the action icon.