Discuss moving all mod-file output to folder `M_.dname`

The discussion in !1793 (merged) points to a design problem of the generally useful M_.dname-option: We still save various output-files like the _results.mat-file in the main folder. So the dname-saving logic does not fully work. In the long-run, we will move almost all Dynare-generated output to a subfolder of M_.dname to get a clean root directory. We have increasingly moved to the direction in the past, e.g. with the $\LaTeX$-files. Two notable exceptions will most probably be

1. _TeX_binder.tex due to \include only working for subdirectories
2. The log-file
3. Potentially the files generated by mode-finders as the user can easily turn them off.

Still to be done:

• Offer a preprocessor command line option dname to set this at the preprocessor-level. This would allow solving the json-issue discussed at !1793 (merged)
• Move the JSON files