Create a river

* Shows the create river form in the header modal.
* Redirects user to the river when successfully created
Merge branch 'ui-dev' into rivers-ui-dev
Display channels modal.

* Display list of channels in a river when channel settings clicked in
drops listing.
Add Channels

* Add channels modal implemented.
* Pending opml import, busy and error messages.
Delete channel from add channels modal.

Clicking on the 'X' removes the channel.
Modify Channel

* Editing a channel from the channels modal implemented.
Display channel list on river drop listing

* Filtering the drop list depending on the selected channels is pending
Added static river settings pages.
River Display Settings

* Allow update of river name, privacy and description.
* System message ui added to signal success/failure
Error Handling

* Throw different types of expceptions per api error.
Infinite scrolling

* Returned page parameter
* Backbone fixes. add parameter is now update during fetch + issue with
comparator for drop list sorting.
Activity view cleanup
Filter content by type

* Implemented filtering of content (user assets) by type i.e.
limiting the "All" tab to either buckets or rivers. Refs #320
Login: Display errors as system messages.
Filter assets by role

* Implemented filtering of rivers and buckets in the content
view using the roles tabs i.e. "All", "Managing" and "Following"

* Added AssetList#following in assets.js for filtering the asset list
based on the 'subscribed' property
New drop polling

* get_drops_since implemented in river service
* seems there is a change with how Backbone iterates on models added to
a collection for the add event. Models are iterated over in the order
they are added and not their natural order. Reversing the droplist in
Controller_River::action_droplets to resolve this for now.
Logout on authorization exception.
Delete assets from content view

* Implemented deleting of assets using the "Delete" button
on the content view in the user's dashboard. A delete action
triggers a confirmation message and a subsequent (success) system
message when the action is confirmed and successfully performed.
Refs #320
Merge branch 'dashboard-content-dev' into integration-dev

Conflicts:
	modules/SwiftRiver_API/classes/SwiftRiver/API.php
	modules/SwiftRiver_API/classes/SwiftRiver/Client.php
	themes/default/media/css/styles.css
	themes/default/media/js/assets.js
	themes/default/media/js/drops.js
	themes/default/media/js/global.js
	themes/default/views/pages/drop/js/drops.php
	themes/default/views/template/nav/header.php
Fix photos view