improve Doxygen documentation

- dox and dox-install target in Makefile
- doc/layout.xml
- doxygen groups
  - programs with @ingroup Program
  - features with @ingroup Monitors, @ingroup FCT
Merge branch 'master' of github.com:jgressier/typhon
improve doxygen documentation for FCT modules
[bugfix] OpenMP private variable in NS boco wall computation
Merge branch 'master', remote branch 'origin'
Merge remote-tracking branch 'origin'
improve Doxygen documentation with @todo @bug and @dev
update of non-regression files after improvements of high order boundary conditions
CGNS configuration available with CMAKE
Merge branch 'master' into 'cmake'