deliteful/ScrollableContainer

Contains:

* A container widget with scrolling capabilities (using delite/Scrollable).
* Intern unit tests.
* Functional tests.

Depends on the following pull request:
* https://github.com/ibm-dojo/delite/pull/79 (delite/Scrollable mixin)

The functional tests (and only them) additionally depend on:
* https://github.com/ibm-dojo/delite/pull/75 (DisplayContainer/DisplayController etc.)
* https://github.com/ibm-dojo/deliteful/pull/7 (ViewStack/LinearLayout etc.)
(these dependencies are due to the use in these tests of deliteful/LinearLayout).