WIP: Admin dashboard - #240

Still working on it, but I reckon now is a good time to start getting some comments.

See http://i.imgur.com/omyqKDI.png for a screenshot.

References #240 

**TODO**

- [x] Move dashboard code into Dashboard plugin
- [x] Add ability for user to collapse blocks
- [x] Ability for user to change block order
- [x] Ability for user to change block size (Within limits) (User has option of full width, or half width)
- [x] Identify and create useful blocks for core plugins - These will be created in a stand-alone plugin.
- [x] Trigger pre- and post- render events