My suggestion for the last code clean up

These are my suggestions for the remaining code clean ups before the next release.

Since I've also used tools to check the source I think we should now found all problematic or unused parts and this should be hopefully completed.

To be complete: From how FindFwhm (in core/peakfit/fit_models.cpp) is implemented and used I got the conviction that it should put into a local namespace. This seems to be in line with the rest of the steca source code. However, I have not changed this yet.