Added collaboration invite notification email
Notify asset owners when collaboration invite is accepted.
Fix changes missed out in 89900af7

* RiverList, BucketList and BaseAssetListView were moved to a module
* Visitor can now see buckets/rivers specific listing i.e.
http://<domain>/account_path/{rivers|buckets}
Move River/Bucket follow/unfollow to their respective controllers

* Previously duplicated between the River/Bucket controllers and User
controller.
Update global Bucket/River list on Follow/Unfollow

*ux +1
Update 'followers' count when user followed.
Notify on new follower.
Added markdown module
Cleaned up bucket discussions

* Renamed Comments and Comment_Scores to Bucket_Comments and
Bucket_Comment_Scores
* Tidied up the JS to rely on backbone's events.
Notify bucket owner and followers on new comment

* Also allow followers to comment on public buckets
Reinstate ae5da163

* Kohana 3.3 Request objects have the _controller member populated
when the execute method is called and not during constuction. Thus the
need to use the uri method now instead of controller.
Notify river/bucket owner and followers on new drop comment
Made new collaborators read only until invite accepted

* is_owner() will be false but is_collaborator() will be true until
collaborator_active = 1 for editor collaborators.
New and improved activity stream

* Added new activities (create bucket/river, follow bucket/user).
* Removed activity_stream database view
* Activities stream improved now with infinite scroll and updates.
* Activities js now static. #212
Made channels js static. Closes #212
Allow comment replies via email

Comment notifications are now sent with a token from address. There is
also a drop/bucket comments api end point.

These two additions allow an MTA to be configured to post comments
received via email to the end points.
Merge branch 'master' into email-notifications-dev
Change "url" references to "URL"

* Users were unable to change their email or reset their
password when the authentication backend is RiverID. This
is because the class (Model_User) that generates the url for
resetting the password was still referencing the url helper as
"url" instead of "URL"after the Kohana 3.3 upgrade. Closes #308
Change Array to lowercase array
Change "url" reference to "URL"

* This is a Kohana 3.3 compliance fix