Missing parameter handling

The fork implements a basical parameter checking both in the editor and at runtime.
The editor highlights calls / tests with missing parameters where as they fail a test run with a helpful error message at runtime (providing file, line and parametername if available).

For this the 'optional' attribute of the ```@FixtureParameter``` gets evaluated and every non-optional parameter which is missing is a validation error.
This helps a bit with issues #7 and #9 but don't closes them completely - as primitive types can still be declared optional, which would lead to the same error.
However fixing those issues based on this fork would be just implementing an additional validation rule that checks for this invalid combination.

Note that I had to adapt a few test cases which relied to run without specifying the complete mandatory parameter set. I declared those parameters explicitly optional in the fixtures now.
Also note that there are checkstyle validation errors concerning the 'methodName' rule, where I used polymorphical dispatched methods and declared them with a leading '_' analogous to XText.