gimp-app:
Depend on glib-networking [2], which is used for https connection.
Fix plist when default-off options are enabled [1].
While here overhaul dependancies.

py-gimp:
Fix a issue with unresolved symbols in the python library, due to incorrect linking.

PR: 232066 [1], 232047 [2]
Reported by: bsd@dino.sk [1], rsmith@xs4all.nl [2]