Fixes to support Python 3

Some fairly basic changes to make the code work with Python 3. It still runs fine in Python 2.7 as well (and should run fine in 2.6, but I haven't tested that).

One of the tests will fail until this fix is merged into Pyramid: https://github.com/Pylons/pyramid/pull/1032

Of course, it could also be fixed by changing line 79 of betahaus/viewcomponent/models.py from

    if va.containment and not find_interface(context, va.containment):

to

    if va.containment and find_interface(context, va.containment) is not None: