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.
Though it's not the best solution, a workaround with this PR pretty much as-is is to set the log level to ``DEBUG`` via ``qutip.settings``, then for the user to add filters in the traditional Python way before calling anything that uses that logger. Each QuTiP logger is created with the module name, so it's not too hard to filter messages instead of using a global log level.