Enhancement: Improved collaborators column in shared file lists

Fixed issue with the collaborators column where only one was being displayed in the "shared with you" file list.
This is done by properly aggregating all share entries under each file entry for the list, which now
also includes group shares and link shares.

Improved the look of the collaborators by adding avatars and icons there for the shares in the collaborators and owner columns.

https://github.com/owncloud/web/issues/2924
https://github.com/owncloud/web/pull/3049
