Remove unused options / improve options

[mknaranja]

The current implementation has a lot of options (https://github.com/mknaranja/GMGPolar/blob/main/include/constants.h) refactored from the experimental Matlab code whose features where not refactored since only the most important and best working options have been transferred to C++. Unused options and all its references should be removed.

Among these options are:

• origin_NOT_coarse
• plotit (-> or better replace it by some option to export the solution in a meaningful format)
• paraview

For the options, we should think of making use

• solveit --> use it to define if compute_error() is executed?!

(To be extended)

[mknaranja]

At some point of the code, there are snippets "alt: ..." There an alternative option would need implementation. We should decide for each option if we do so.