Printer profile added in Preferences for soft-proofing

The output profiles now retain only 'Display' device class as well as
the Monitor profile - and they both have to have rgb color space, the
printer profile retain only 'Output' device class.

MacOS can use soft-proofing but due to undocumented feature of OSX, and
since Cairo assume that the image data are sRGB, the monitor profile is
forced to 'RT_sRGB'. A warning message replace the combobox for this OS.

rtgui/preferences.h

@@ -95,6 +95,9 @@ protected:
     Gtk::CheckButton* showExpComp;
 
     Gtk::FileChooserButton* iccDir;
+    Gtk::ComboBoxText* prtProfile;
+    Gtk::ComboBoxText* prtIntent;
+    Gtk::CheckButton* prtBPC;
     Gtk::ComboBoxText* monProfile;
     Gtk::ComboBoxText* monIntent;
     Gtk::CheckButton* monBPC;