updated bioreactor classes
updated bioreactor class
updated ex_dfba
added Batch and IdealFedbatch classes to bioreactor module
added a new dfba example
debugged bioreactor module
cosmetic changes to ex_dfba2
cleaning up examples directory
Merge branch 'kai-branch'

Conflicts:
	examples/ex_dfba2.py
Changes in core.transformation. Small update in MOMA.
reorganized bioreactor

broke bioreactor.py into base.py and bioreactors.py

base.py contains the base classes
bioreactors.py contains the subclasses of Bioreactor

future: strains.py contains the subclasses of Organism