Clean up the CMake code around the python modules and uninstalling

 - It isn't possible to build python extensions using distutils that
   link to things that we are building, because CMake provides no
   means for a custom command to depend on a library. Build them
   using CMake directly instead
 - Clean up the tests: the tests depended on having a working opengl
   and core plugin xml file and were also sensitive to xml data. Make
   a mock.xml and use that instead
 - Require ini for the compizconfig-python tests. They won't run without it
 - Fix the uninstall scripts. We were clobbering the uninstall target
   with the python uninstall targets, that is just plain wrong. Created
   a new cmake function to append custom uninstall scripts to the global
   uninstall script