libraries  and test source folder added

1) Libraries added to the projets lib directory and to the classpath.

2) A directory for the test sources was added.
In there a Example class for the imported libraries can be found.

3) The core package name was changed to at.tetris4j.

Added libraries (inclusive dependencies):

Testing:
-JUnit
-Mockito

Logging:
-Logback (SLF4J)