Remove fake DICT support

We depend on a version of LCMS2 that has dict support now.
Add a way to set the CdIcc filename manually

This may be required if the CdIcc object has been loaded from an on-disk cache.
Add cd_icc_save_default() to save a profile to the default location
Remove the ICC volume searching functionality

It never worked by default, and it was odd to have profiles only available when
the external volume was _manually_ mounted. It's better just to import the
profiles by double clicking on them and having them always available.