Make drop down tool work with generic toolbars

Objective:

* Remove ve.ui.DropdownTool's dependency on ve.ui.SurfaceToolbar so it
  can be used with any ve.ui.Toolbar

Changes:

ve.ui.DropdownTool.js
* Bind onBlur to document mousedown in capture mode instead of trying to
  add more and more things we are listening to which is a losing battle
* Refactor activate/deactivate mode changes
* Get rid of isEnabled check - surface should disable toolbar, the tools
  shouldn't be checking if the surface is enabled after the fact (also,
  this is harmless and doesn't change any actual interactions)

Change-Id: I738209d17649358c2f9812f9abac576960af867b
Cleanup tool styles

Objectives:

* Make drop down tools look more like buttons and less like inputs, since they aren't text input and are buttons
* Make context toolbars inside surface widgets render correctly
* Show outlines of groups on hover to hint tool relationships
* Make neighboring active tools look cleaner

Changes:

ve.ui.Tool.css
* Merge ButtonTool and DropdownTool styles as much as possible
* Add styles for DropdownTool active states
* Only round the corners of the first and last tool in a group
* Soften the borders between consecutive active tools

ve.ui.Toolbar.css
* Add border to groups on hover

ve.ui.Widget.css
* Isolate surface widget toolbar styles by using stricter selector

ve.ui.Tool.js
* Fix incorrect capitalization of class name

ve.ui.SurfaceWidget.js
* Add classes to toolbar and surface for better style targeting

Change-Id: Ib5ae8f705ef1e9c481e5bdf8c8dcef9c1eb22c4d
Add ve.ui.ToolGroup and use within toolbar setup

Objectives:

* Use a class for toolbar groups to add more functionality later
* Rename addTools method to setup

Changes:

*.php
* Add link to new file
* Move ui element classes up for more general use

ve.init.mw.ViewPageTarget.js, ve.init.sa.Target.js, ve.ui.Context.js,
ve.ui.SurfaceWidget.js
* Update use of addTools method

ve.ui.Tool.css, ve.ui.Toolbar.css
* Move styles between sheets

ve.ui.Toolbar.js
* Rename addTools to setup
* Use ve.ui.ToolGroup objects when building tools

ve.ui.ToolGroup.js
* New class, encapsulates tools

Change-Id: Ic3a643634a80a8ac7d6f6f47f031d001c7efaee7
Merge changes Ic3a64363,Ib5ae8f70,I738209d1

* changes:
  Add ve.ui.ToolGroup and use within toolbar setup
  Cleanup tool styles
  Make drop down tool work with generic toolbars