There is no non-hackish way of fixing this without adding a new
"use-opacity-paint-mode" property to GimpToolPreset and a new toggle
in GimpToolPresetEditor. Restoring opacity and paint mode can now be
controlled explicitly, and defaults to TRUE.
We don't need a standard tool-preset object, so just remove the
code that was copied and pasted from other GimpData objects.
Fixes the crash on startup in non-interactive mode.
- add "Gimp" property to GimpToolPreset
- implement GimpConfigInterface::deserialize_property() and deserialize
the "tool-options" locally so we can pass the required "gimp" construct
property.