A lot less lines for the same functionalities!
This includes improvements too:
* "include-pointer" as new PDB argument;
* settings storage thanks to GimpProcedureDialog;
* it should hopefully work better in non-interactive (though it's untested).
The macOS and Windows screenshots are untested after this change, though they
should still work the same. Please report if there is any problem!
Add error reporting to all screenshot backends, but only really use it
in the gnome-shell backend: check all DBus calls for errors instead of
crashing.
Also fix detection if gnome-shell is running: just creating the
GDBusProxy always succeeds, so call org.freedesktop.DBus.Peer.Ping
on the newly created proxy.
Some more abstraction in the screenshot plug-in, now allows for
runtime backend selection. Add stubs for the gnome-shell backend,
registers itself as unavailable because it's still unimplemented.
Move OS X and X11 specific code to its own files, to prepare for more
shooting backends being added. Also remove unimplemented G_OS_WIN32
stubs, if anyone feels like implementing a Windows backend, by all
means go ahead.
Jehan