Fix bug 5763 - Largest fitting font logic in Sidebar title causes
	font criticals.  Cleanup some related stuff in the process.

	* libnautilus-extensions/nautilus-font-factory.h:
	* libnautilus-extensions/nautilus-font-factory.c:
	(nautilus_font_factory_get_font_by_family),
	(nautilus_font_factory_get_font_from_preferences):
	Move these functions to nautilus-gdk-font-extensions.[ch].

	* libnautilus-extensions/nautilus-gdk-font-extensions.h:
	* libnautilus-extensions/nautilus-gdk-font-extensions.c:
	(nautilus_gdk_font_get_largest_fitting), Rewrite the function to
	not depend on any hard coded font sizes or XLFD names.
	(nautilus_gdk_font_get_name), New function.
	(nautilus_gdk_font_get_size_in_pixels), (unref_fixed_font),
	(nautilus_gdk_font_get_fixed),
	(nautilus_gdk_font_xlfd_string_new), Move these 2 here from
	nautilus-font-factory.
	(nautilus_self_check_ellipsize_start),
	(nautilus_self_check_gdk_font_extensions):
	* libnautilus-extensions/nautilus-scala...