Rearrange old unittests.py; Use nosetests

Hello Holger, 

in order to get the tests running (and to get a base for adding more tests) i moved the unittests.py to a sub directory "tests/" in which nosetests searches for tests. I also added a configuration for nosetests that writes a test coverage report (the coverage report is saved in build/html). 



* Move unittests.py to tests/ subdirectory
* Split out dependencyparser test to an extra file
* Add configuration for nosetests
* Use nosetests in Makefile target "check"