compatibility check:
A release Slic3r is not compatible with alpha and beta configs,
a beta Slic3r is not compatible with alpha configs, but is compatible
with beta configs etc.
Added Version Index "version" method.
Implemented automatic selection of default_print_profile and
default_filament_profile, when the print / filament profiles are
not compatible with the selected printer profile.
Fixed selection of a printer profile, if the currently selected
printer profile becomes invisible.