enabled some clang-tidy warnings for non-GUI code

[firewave]

There are some clang-tidy warnings which cannot properly handle the extensions used in the Qt code so the produce lots of false positives and were previously enabled. With clang-tidy now offering the possibility to inherit the parent configuration we can enable these across the project and simply disable them for the GUI code.

No additional warnings were found as they were already fixed in earlier commits without enabling the checks in question.

[firewave]

The checks also seem quite light:

   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
[...]
   0.0166 (  0.4%)   0.0303 (  0.4%)   0.0469 (  0.4%)   0.0473 (  0.4%)  readability-convert-member-functions-to-static
[...]
   0.0109 (  0.2%)   0.0252 (  0.3%)   0.0360 (  0.3%)   0.0360 (  0.3%)  readability-redundant-access-specifiers