Contains templates, clipart galleries, palettes, symbol font etc.

How-to add a new gallery:
	+ create a directory extras/source/gallery/foo/
	+ create a .str file extras/source/gallery/foo/foo.str
	+ add a [foo] section to extras/source/gallery/share/gallery_names.ulf
	+ add a Gallery_foo.mk at the top-level (and mention in Module_extra.mk)
	+ add a new GALLERY_FILELIST statement in scp2/