Add a remove_from_config utility

* This enables to remove from the udtc config file any registered framework
* Add corresponding tests
Add removal feature to frameworks

* All frameworks have now a --remove option enabling them to uninstall
  their desktop file, icon, projected content and udtc config.
* Add corresponding tests.
Fix tests mocks to be instantiable

* remove() method is abstract, ensure we can continue to register the mock
  frameworks in tests by adding this function.
* Set the args to False when running run_for
Add small tests on calling the remove function
Add 2 reinstall large tests

* This will enable to ensure that recent code change really remove the
  initial installation, even if we change the destination directory.
Add some comments and FIXME