fix running of 'easyconfigparser' and 'format_convert' test suites with Python 3

[boegel]

This is mainly about fixing the Wrapper class so it also works with Python 3, but I also stripped out a bunch of stuff that we no longer use (see Patch* and ListOfStrings & co) since some of those tests were failing on top of Python 3.
It was non-trivial to fix those tests, and there's little point anyway in fixing something that is no longer used...
The Wrapper class is still used for the Dependency class (via Convert), so that part is definitely still relevant (for now...).

[bartoldeman]

Ah metaclasses, so much fun there is to be had. I don't completely understand it at first (it's been a long time since I was so deeply into Python classes), but it looks ok, so I will approve.