Adds an icon-pixbuf property to GimpViewable that is used for a default
implementation of new_pixbuf.
Extend gimp_icon_picker to allow the user to pick non-stock icons for tool
presets (or any other class derived from GimpViewable). Icons can come
from any file GdkPixbuf can load or from image data on the clipboard.
- move the code that sets the tool options' "defined" and "serialize"
properties from GimpToolInto to GimpToolOptions so they are always
set correctly.
- make GimpToolOptions fix broken serialized NULL tools automatically.
- make sure a GimpToolPreset's tool options always has a tool set. If all
fails, set a NULL tool explicitly and let the logic in GimpToolOptions
find the right tool.
- set GimpToolPreset's "use" booleans to FALSE for context properties
that have no effect on the tool.
- set GimpToolPresetEditor's toggle insensitive for these properties.
I had to remove the asserrt in tool preset constructor, because with it
it wasnt possible to initalize an empty model object for the editor.
At init time the gimp object passed to the constructor is not yet available.
