modules: fix memory leaks in color-selector-cmyk.c

Also clean up a bit and make the profile label's tooltip show
the profile's summary.
libgimpcolor: add gimp_lcms_profile_open_from_file() and _from_data()

which work just like their lcms counterparts but return an optional
md5 digest of the ICC data and a GError in case opening fails.
libgimpwidgets: use gimp_lcms_profile_open_from_file() in the profile chooser
plug-ins: use gimp_lcms_profile_open_*() in the lcms plug-in

And clean up stuff to pass error messages further up.