loadOmero() improvements

This PR:
- fixes a bug in unloadOmero() (jar removal) and implement unit tests to check Matlab/Java path clearing 
- decouples loadOmero() from connectOmero() and improves the headers to better expose the various signatures
- allow to pass the path to a configuration file directly to loadOmero()
- fixes the ICE_CONFIG reading for loadOmero()
- add various tearDown() methods in unit tests to allow TestUnloadOmero() to be called safely