Added documentation an __repr__ function to PseudoDotDict.
Added lots of stuff:
CCBase now has __repr__, __mul__, __div__, __add__ and __pow__ functions
that it gets from self.expression.

New functionality that ensures that for all CCBase (and child objects),
value always reflects the latest steady-state without having to call
something like _recalculate_value.

display property which returns a nice IPython notebook display object
Made StateKeeper an object (rather than using a class) becuase obviously if
there are more than one symca object it wouldn't work otherwise.
Added save button that comes up on interact() or adjust_figure()
Added some functionality to DotDict and replaced PseudoDotDict in _symca.py and _ratechar.py
with DotDict due to trouble with pickling the PseudoDotDict object.