Added new logging and settings support, started refactoring debugs.

This change enables the use of Python standard logging, and backs it by a new qutip.settings entry. A few instances of classic ``if debug: print`` style logging have been refactored. The new ``qutip.settings`` entry is based on [configobj](http://configobj.readthedocs.org), with a fallback to classic ``~/.qutiprc`` parsing if that library is not available. Errors in the new functionality introduced by this commit are also logged, and can be accessed by setting up ``logging.basicConfig`` *before* importing QuTiP. The optional configobj dependency should almost always be met, since it's shipped with matplotlib.
Use 

    from __future__ import absolute_import

to make to activate absolute imports in python 2. In Python 3 your code already behaves correctly: when you do "import logging" you get the standard library, when you do "import .logging" or "import qutip.logging" you get the qutip module.