Dashboard configuration - add and remove widgets

In dashboard_config template, get selected status from current dashboard
configuration
In the DashboardConfig view, use containers addWidget and removeWidget
methods to add and remove selections. Destroy shapeshift before and then
call shapeshift after widgets have been added/removed, so that new
widgets are initialized properly. (Triggering rearrange after a new li
has been added has issues see
https://github.com/McPants/jquery.shapeshift/issues/34)
Delegate saving the configuration to parent view method.
In the Home view, remove unnecessary handlers, and add removeWidget
method.