give IEMGUI externals their own copy of the old functions so that the new impl of g_all_guis.c can evolve freely

improved installer to avoid install of Gem libraries when doing incremental install (should significantly shorten incremental installs)

further cleaned-up ggee/image selection logic (now the selection does not incorrectly pick up on the parent GOP selection, so that when opening subpatcher it does not show up as selected

improved ggee/image to have a default empty image and ensured that its layer ordering is preserved after loading a new image. Finally, made a check for valid images--if invalid format, the image reverts to default empty image included in the ggee.

*enabled drag'n'drop in the main window/console, as well as patches
*implemented properly supported horizontal touchpad scroll (in addition to vertical and shift+vertical, which is being handled as horizontal)
*pd-gui fails to start (missing pd-l2ork in the $lib/bin/ directory)