refactoring and improvements

- add --modules= switch to specify which modules should get tested
- return the exit code from the tests, if multiple exit codes are found, the first unequal to 0 will be returned
- simplified indexcontroller

resolves:

https://github.com/prolic/HumusPHPUnitModule/issues/15
https://github.com/prolic/HumusPHPUnitModule/issues/7