Bugfix: Moved resharers to the top of owner collaborator entry

For received shares, the resharers user display names are now shown
on top of the owner entry in the collaborators list, with a reshare
icon, instead of having their own entry in the collaborators list.

This makes the reshare situation more clear and removes the ambiguity
about the formerly displayed "resharer" role which doesn't exist.

https://github.com/owncloud/web/issues/3850
