highlight shares in the stream and unshare deletes share-actvity and remove it from the web-ui

- highlight shares in webUI
- if unshared delete the activity for a share.

result: http://blessuren.de/pics/unshare.png

I disable the unshare button on the original post cause you maybe want to share the note again to other people;lists;groups
share to specify target: http://blessuren.de/pics/share_note.png 
https://github.com/e14n/pump.io/pull/991