Tool and context menu size and alignment fixes

Objectives:

* Make context menu toolbar consistently sized and aligned, especially
  in monobook

Changes:

ve.ui.Toolbar.css
* Remove vertical line between groups, just use whitespace
* Switch from padding to margins to avoid size calculation issues

ve.ui.Tool.css
* Remove tiny margin on button tools, tightening them up a bit
* Replace 50% 50% with center center

ve.ui.Context.css
* Switch from padding to margins to avoid size calculation issues
* Use different margins depending on text direction
* Reverse the 0.8em rule used in the dialog - this is a hack, it should
  be cleanup up later with a better strategy for normalizing the size
  of text within VE elements

Change-Id: If65f12382625efa33777e284bd23a94dc509436a
Merge "Tool and context menu size and alignment fixes"