Extend Solver Independent SMTLib2 Parser/Generator

[baierd]

This PR extends JavaSMT with an independent SMTLib2 parser/generator layer.
Every solver can use the layer to generate or parse SMTLib2, independent of their own implementation.
The parsing directly uses the API of the solver.
Generating tracks all API usage independently into SMTLib2.

Additionally, we offer a complete solver-independent layer, that is usable with no solver installed. This layer can generate SMTLib2, but also parse SMTLib2 to manipulate the given formula.

Ideally, we also want to support usage of the solvers binaries with SMTLib2 directly. This has been tested for Princess, but has not been implemented for all solvers. My suggestion would be to remove/extract it from this PR and work on it separately.

TODO:

• Add a full visitor implementation for the solver-independent layer.
• Transform the layer into a delegate.
• Add appropriate options for the generator/parser.
• Check if its possible to clean up the auto-generated files from ANTLR, or generate them when building the project (similar to the other auto-generated files).