Added ``is_ass()``, ``has_ass()`` methods to ``FileReferenceExtension`` class.
set houdiniEnv to use PyQt4 by default
fixed Qt lib load in version_updater
Removed Shallow Reference Updates
After having punched in the face by the reality of not being able to store the result of shallow reference updates, I've updated version_updater to the oldest version, where it is not possible to do any kind of deep update but only first level references. But at least it is able to show which version needs to be updated.

The next series of commits will probably about Scene Assemblies.
fixed an error for PyQt4
- Updated the tests for the new 1st level reference  update interface
- Implemented a custom QStyledItemDelegate for showing one column of the VersionTreeView as a button (but will remove it and add a context menu instead)
- Added a custom context menu to help the user to open the listed version in a new Environment instance.
Merge /home/eoyilmaz/Documents/development/anima/anima

Conflicts:
	anima/ui/models.py
removed the custom delegate again, which was reintroduced in the last merge
fixed ``version_updater.open_version()`` method to correctly use the ``version.absolute_full_path``
update and create are now using two different colors in version_updater ui
version_update UI now refreshes after a version is updated
fixed version_updater.py

fixed version_updater.py for getting an intermediate reference resolution
from the environment in every reference update.
fixed version_updater column labels and context menu problem
Merge /mnt/T/DEV/tmp/anima