Bugfixes in the matlab part and addition balance check for S

I fixed some bugs in the matlab code. Notably there was a severe bug in  createKeggModelFromS after line 25, which messed up the cid to inchi mapping if any compound was in kegg additions and the model cids.

Further I added the balanceReactionsS function in matlab, that checks if reactions are balanced and sets all reaction coefficients to 0 if the reaction is unbalanced. The same functionality was added to KeggModel in python.

There is an examples in /examples/vz how to use the functions. Also the examples show how the component contribution method can be run with a stoichiometric matrix file as input. The example runs fine in the matlab version, but returns dubious results in the python version. Probably there are still bugs in the python script.

Some kegg_additions were added to the kegg_addition files, which are required to run my examples.