Added class MultifusionInf.
Added AlphaExpansion and Random multi-proposal generator.
Fixed multifusion method, added python bindings.

FactorMapper:
* Changed variable type from size_t to IndexType.

GraphicalModelBridge:
* Some functions now return by reference argument.
* Added method to translate a state from old to new model.

MultifusionInf:
* The current best vector is added to the fuse proposals.

Added python bindings.
Changed BridgeStorage, so no more std::find is needed.