Change default processing log folder to the case folder

[lfcnassif]

This is an old idea. Although it is possible to redirect the log file using the -log command line option, saving it into the case folder by default has some advantages. Not sure if we should also keep the old log location, duplicating the log. Thoughts?

[gfd2020]

My graphical interface does something similar. At the end of the processing, the GUI copies the processing log into the case folder. It's very useful; it makes traceability easier.