Update share action text to display owner/recipients

- when a share was changed, update the share action text
- added file data attribute "data-share-recipients"

@owncloud/designers this is to add the name of the recipients behind "Shared" in the "Shared with others" list.
It also auto-updates that label when changing the share settings. (which never worked in the past)
I used the format suggested here: https://github.com/owncloud/core/issues/8301#issuecomment-41293079

Also, when sharing with link it will add "Public" in front of it.

Please have a try while I fix bugs and write unit tests.

TODO:
- [x] Make it a maximum of 4, not 2
- [x] Fix label update to use display names 
- [x] Unit tests for share.js and OC.Share changes