GfxState: substitute manual ref counting in GfxColorTransform by shared_ptr
This patch as said replaces the manual ref counting in GfxColorTransform. Along the lines it also introduces another shared_ptr with custom deleter for cmsHPROFILEs, which is named GfxLCMSProfilePtr.
This merge request is based on the merge request !553 (merged).
Thx for reviewing