Move Contained functionality to Container.
Removes Contained class completely.
Also make Container extend Widget.
fix css naming of shared button* classes
Squashed commit of the following:

commit ec8757d9cbc6ab59b4a2ed56e06b0ab2c4a5a562
Author: Adrian Vasiliu <vasiliu@fr.ibm.com>
Date:   Mon Jan 13 17:03:44 2014 +0100

    Taking into account Bill's comments

commit 9bb02a4c41847b9cbe1ab53132a9b281aaa4bc46
Author: Adrian Vasiliu <vasiliu@fr.ibm.com>
Date:   Thu Jan 9 17:02:07 2014 +0100

    delite/Scrollable mixin
update CssState tests following css renaming
register(): don't require _introspect() method.

register() should take any class.
The class can optionally have createdCallback() and enteredViewCallback() methods,
but it shouldn't need an _introspect() method.

Refs #81.
parse() should just no-op when no widgets are registered
remove unused file and reference to image that no longer exists
fix a11y test failure (on FF)
small cleanups
improve doc + make sure if someone change a property in the refreshRendering method the list of invalidated properties is not entirely cleared
ibm-dojo --> ibm-js
enable requirejs for unit tests
add DisplayContainer and defaultapp.css

take bill's comments into account
improve documentation + rename some parameters and a property to be clearer on their intend