Alien extensions

VisualEditor.i18n.php, VisualEditor.php
* Button title
* New experimental files

ve.*.MWAlienExtensionNode.js
* Very basic extension of ve.*.MWExtensionNode

ve.ui.MWAlienExtensionInspector.js
* Default to inline-block for wrapper. Should probably
  get rid of styled wrappers for GeneratedContent eventually.

ve.ui.MWAlienExtensionInspector.js
* Basic extension of MWExtensionInspector. Override title to
  use tag name e.g. '<easytimeline>'. Could be changed in future
  to 'Extension: easytimeline' or similar.

*.png, *.svg, *Icons*.css, ve.ui.MWAlienExtensionButtonTool.js
* Angle bracket icon for button (open to suggestions)

ve.ui.MWInspector.css
* Make extension inspector text input tall by default.

Change-Id: I07f0686839192cad3cd8dfd3233ae907fe5cdf6a
Merge "Alien extensions"