TravisCI integration and updated test suite (#296)

* Make TravisCI setup

* Use pytest, move tests to seperate files

* Added system to check if `onX` events were successfully executed

pytest.ini

@@ -0,0 +1,6 @@
+[pytest]
+xfail_strict=true
+markers =
+    offline: Offline tests, aka. tests that can be executed without the need of a client
+    expensive: Expensive tests, which should be executed sparingly
+addopts = -m "not expensive"