The Great ve.ui.Surface refactor of 2013

Prologue:

Farewell ve.Editor my good chap… Oh, hey there HTML frames - I didn't
see you there! In a world where iframes are outlaws, and symbols like
document and window are global, there were more than a few assumptions
about which document or window was being used. But fear not - for this
commit (probably) tracks them all down, leaving a trail of
iframe-compatible awesomeness in its wake. With the great ve.ui.Surface
now able to be used inside of iframes, let the reference editing
commence. But there, lurking in the darkness is a DM issue so fierce it
may take Roan and/or Ed up to 3 whole hours to sort it out.

Note to Roan and/or Ed:

Editing references seems to work fine, but when saving the page there
are "no changes" which is a reasonable indication to the contrary.

Objectives:

* Make it possible to have multiple surfaces be instantiated, get along
  nicely, and be embedded inside of iframes if needed.
* Make reference content editable within a dialog

Approach:

* Move what's left of ve.Editor to ve.ui.Surface and essentially
  obliterate all use of it
* Make even more stuff inherit from ve.Element (long live this.$$)
* Use the correct document or window anywhere it was being assumed to be
  the top level one
* Resolve stacking order issues by removing the excessive use of z-index
  and introducing global and local overlay elements for each editor
* Add a surface to the reference dialog, load up the reference contents
  and save them back on apply
* Actually destroy what we create in ce and ui surfaces
* Add recursive frame offset calculation method to ve.Element
* Moved ve.ce.Surface's getSelectionRect method to the prototype

Bonus:

* Move ve.ce.DocumentNode.css contents to ve.ce.Node.css (not sure why it
  was separate in the first place, but I'm likely the one to blame)
* Fix blatant lies in documentation
* Whitespace cleanup here and there
* Get rid of ve.ui.Window overlays - not used or needed

Change-Id: Iede83e7d24f7cb249b6ba3dc45d770445b862e08