[#316] Disable follower lists

Disable follower lists for normal users

Make it so that only sysadmins can see a dataset, user or group's list
of followers.

Add auth functions to user, dataset and group follower_list functions.

user controller, group controller, package controller:
  /followers pages send 401 if not authorized

Remove followers tabs from user, dataset and group pages.

Some tests need to be fixed now
[#316] Update follower api tests

Make it pass a sysadmin's API key whenever calling *_follower_list,
since only sysadmins are authorised to call that now.
[#316] Update follower frontend tests
[#316] Add tests for new follower list auth
[#316] Remove "started following" activities
[#316] Update activity streams API tests
[#316] Update activity streams frontend tests
[#316] Add auth for followee_list APIs

Don't let visitors or other users see what a user is following.
Merge branch 'master' of github.com:okfn/ckan into 316-disable-follower-lists
[#316] Removed 'follow dataset' and 'follow group' activities

Forgot to remove these in earlier commit
5c7e022a09798d02b1fd30356517a9ef071d0577
[#316] Update user dashboard tests
[#316] Update some more activity streams tests
Merge branch 'master' into 316-disable-follower-lists
Merge branch '316-disable-follower-lists'