re #428: Move WIRIS editor into dialog view.

Instead of popping up a new window for the CKEditor WIRIS plugin,
contain it in a Backbone view with dialog-esque chrome and an
iframe in the middle, with some shims to satisfy the plugin's
assumptions about being in a pop-up window.

Half of this change is in the 'web-client' repository, and the
other half is in the 'ckeditor' repository. They can't live without
each other.

Outstanding:

- Hook up our dialog buttons to trigger the WIRIS plugin's buttons,
  so it can perform all its usual communication with the CKEditor
  instance back on the main page when you click those.
- Hide the WIRIS plugin's ok/cancel buttons.
- Hide the CKEditor toolbar when showing the WIRIS editor.
- Hide all the cruft we don't want from the WIRIS plugin (e.g. the
  help icon that just goes to a marketing page.)
- Make it pretty and more touch-friendly.