Various updates needed for this add-on

[pgrunewald]

Hello,

this add-on has various problems:

• It depends on bootstrap.py which tends to date very fast. Better replace it with virtualenv and requirements.cfg (similar to buildout.coredev)
• freedesktop.org.xml is outdated. Additionally when using the latest one, the parsing breaks.
• Tests can be improved (add relevant cases, remove irrelevant cases, test fixture bases on plone.app.contenttypes without being necessary)

I am planning to address the aforementioned problems with an upcoming PR and that's why I created this issue.