Story 1628: Put toolbar in header of VE overlay

* Add template partial so VisualEditor overlay can have different
header from EditorOverlay
* Ship our own toolbar styles with VE
* Disable link inspector for time being

Dependency: I4c72b4b9128b3a74de8b8b5bce7664fbb315216b
Note:
Without I26f31de859bec04db11e9fa050c4fa9f52f4e3ff styles
may look slightly odd but they will still be functional.

Change-Id: I20b1f9e5d57dc03d26ba591ff94d949dcfb43ba1
Merge "Story 1628: Put toolbar in header of VE overlay"