Solver: Support for French added

Based on a request I received recently I decided to let the solvers learn an additional language. Now the Vigenère Solver as well as the Substitution Solver support French as well. Thus they master more languages than I do.

Implementing another language was straight forward as internally just a set of frequency tables was added.

If you feel the results are not that accurate, please let me know. I am not 100% sure I am treating the non-latin characters in the best way.