Tests for container token rendering in machine panel.

There have been minor changes to machine-panel-view to make it easier to tests;
specifically, the duped code rendering container tokens in the regular and the
bare metal case has been broken out into its own method, which can be stubbed.

The test file, test_machine_view_panel.js, has been modified a lot.
* Tests have been reordered to put similar tests together, so it's easier to
  determine what has and has not been tested, and test like things via one
  describe block. e.g. all the drag/drop tests (including those about listening
  to events) are now part of a 'token drag and drop' describe block. I've noted
  inline where tests have just been moved without being altered.
* Many tests have been added for the machine panel view's rendering of
  containers.