Context, frame, window, dialog and inspector refactor

This is a major refactor of user interface context, frame, dialog
and inspector classes, including adding several new classes which
generalize managing inspectors/dialogs (which are now subclasses
of window).

New classes:
* ve.ui.Window.js - base class for inspector and dialog classes
* ve.ui.WindowSet.js - manages mutually exclusive windows, used
  by surface and context for dialogs and inspectors respectively
* ve.ui.DialogFactory - generates dialogs
* ve.ui.IconButtonWidget - used in inspector for buttons in the head

Refactored classes:
* ve.ui.Context - moved inspector management to window set
* ve.ui.Frame - made iframes initialize asynchronously
* ve.ui.Dialog and ve.ui.Inspector - moved initialization to async
  initialize method

Other interesting bits:

ve.ui.*Icons*.css, *.svg, *.png, *.ai
* Merged icon stylesheets so all icons are available inside windows
* Renamed inspector icon to window

ve.ui.*.css
* Reorganized styles so that different windows can include only
  what they need
* Moved things to where they belonged (some things were in strange places)

ve.init.Target.js, ve.init.mw.ViewPageTarget.js, ve.init.sa.Target.js
* Removed dialog management - dialogs are managed by the surface now

ve.ui.*Dialog.js
* Renamed title message static property
* Added registration

ve.ui.*Inspector.js
* Switch to accept surface object rather than context, which conforms
  to the more general window class without losing any functionality
  (in fact, most of the time the surface was what we actually wanted)

ve.ui.MenuWidget.js, ve.ui.MWLinkTargetInputWidget.js
* Using surface overly rather than passing an overlay around
  through constructors

Change-Id: Ifd16a1003ff44c48ee7b2c66928cf9cc858b2564
Merge "Context, frame, window, dialog and inspector refactor"