Create Dashboards plugin to show dashboard boxes.

If Dashboard plugin is not enabled, fallback to ExtensionsDashboards
Add a setupAdminDashboard event
Render dashboard boxes into two columns and a full width column
Trigger event before and after dashboard box render
Add dashboard table to save custom user dashboards
Show some feedback on collapsing a dashboard box
Allow custom sorting of dashboard boxes
Save dashboard box location to database
Load up saved dashboard positions + constant for each column
Some pretty styling when dragging boxes around
Add an example dashboard block.
Remove deprecated Settings::admin_dashboard()
Add Blog feed dashboard widget
Merge branch 'dashboard' into 2.2

* dashboard:
  Add Blog feed dashboard widget
  Remove deprecated Settings::admin_dashboard()
  Add an example dashboard block.
  Some pretty styling when dragging boxes around
  Load up saved dashboard positions + constant for each column
  Save dashboard box location to database
  Allow custom sorting of dashboard boxes
  Show some feedback on collapsing a dashboard box
  Add dashboard table to save custom user dashboards
  Trigger event before and after dashboard box render
  Render dashboard boxes into two columns and a full width column
  Add a setupAdminDashboard event
  Create Dashboards plugin to show dashboard boxes.

Closes #547
Closes #240