Python wrappers

- added SWIG interface file for Python wrappers
- added corresponding elements in CMake build tree
- added WITH_PYTHON option - set to ON by default
Python wrappers

- method fbc::FBAProblem::print() renamed to fbc::FBAProblem::printProblem() to avoid issues with print Python keyword
- added namespace, classes and methods to interface file libfbc.i