Table of contents widget

TOC Widget is created in the mw target view class.
Adding and removing a heading rebuilds the TOC Widget based
on the the order of the page heading nodes.

TOC Widget considers TOC page settings and displays in the default manor
unless forced or disabled.

TOC Widget still needs to be finalized by being placed in the surface.
This could be a problem until we have a CE node for it to live in or
have some DM work added.  Roan and I have discussed how to go forward.

To enable the widget you must add the following to LocalSettings.php:
$wgVisualEditorEnableTocWidget = true;

Change-Id: I488cfbbdb060e50d81f51e0f757e67d0114b8936
Merge "Table of contents widget"