Allow Appending arbitrary Views to Configuration Editor Tab

Add a #view method which takes a view to append to the tab.
Add blank Option to Select Input
Widgets and WidgetTypes

Allow registering new widget types that can be associated to entries
and themings.
Render custom Widgets

Render widgets of widget types associated with an entry in show and
edit views.
Widget Javascript Integration
Editor Widgets Controller

JSON endpoint for editing widgets of entries and themings.
Add Widget Configuration to Editor

Widget type select boxes to edit the widgets of the entry.
Built-in Widget Types

Turn navigation and mobile navigation into widgets that can be
overriden.
Configuring Widgets of Account's Default Theme
Update Widgets in Editor after Sync
Merge pull request #170 from tf/widgets

Widgets and WidgetTypes