packaging-related updates

minor changes related to packaging or testing:

• update version number in setup.py
• introduce __version__ field in __init__.py
• fix test failure because of missing cpptraj even though the test didn't need it
• make ColorSpectrum test case independent of biggles installation
• silence "biggles missing" warning in main __init__.py (errors will be raised when biggles is needed)
• update debian packaging control files
• update dependencies in setup.py