Refactor all conversions

Preliminary:

The math language needs to store all relevant information in the astnodes, and not everything in different symbols, as symbols will change in the next monticore version, and the generated monticore visitor for a language can only be used on astnodes, not on their symbols. (astnode.getSymbol() is deprecated and will be removed soon, so no direct connection between astnode -> symbol anymore; Every symbol needs to habe a unique name for identification)

Conversion:

The conversions should be done using the generated monticore visitor for all astnodes of a language. This includes the optimizations, and general transformations. As the generator currently works mostly with the Math languge symbols only, a huge refactoring is required.

Goal:

Reduce bugs, increase robustness and readability.