Add PDB sample point API similar to how the guide API works. Add core
API similar to the core guide API to make guide and sample point APIs
as similar as possible.
Which will have proper API to deal with an image's color profile (no
parasites, no ICC blobs). So far contains gimp_image_get_color_profile()
and gimp_image_set_color_profile().
Which contains all the API from the "color" group, but with a
gimp_drawable namespace and with support for high bit depths. The
group is actually a copy of "color" with cruft removed and some API
ported to using float instead of integer API.
Deprecated all "color" functions that already have a ported version in
"drawable_color".
This is unfinished WIP, some functions in "drawable_color" still have
the old API.
