Added custom slide projector element class.
Added welcome slide as custom slide.
Added user slide projector element class.
Added clock, countdown ans message projector elements.
Renamed SignalConnectMetaClass classmethod get_all_objects to get_all (private API).
Added migrations to core app.
Fixed and wrote tests.
Updated CHANGELOG.
* seperate unittests and integration tests
* moved old tests in seperat folder 'old'
* created a testrunner that does not create a testdatabase, if only unittests are run
* wrote some unit- and integration tests as examples
* fixed user.get_short_name() to use the sort order from config
* fixed wrong url_pattern in the user app