Merge branch 'master', remote-tracking branch 'remotes/upstream/master'

Merge branch 'master', remote-tracking branch 'remotes/upstream/master'

* remotes/upstream/master:
  diabook-themes: add "community profiles"-box to right_column
  change api.php in function api_item_get_user to check if $usercache is NULL before checking an element in it
  make 'aaa joined group bbb' work from the initiating end, new privacy pref to control it also hidewall wasn't properly checked before sending 'xxx is friends with yyy' messages
  diabook-themes: add "last tweets"-box to right_aside, that searches for #friendica on twitter
  rev update
  start adding tooltips to tab menus
  fix join group notifications

* master: