libgimp: 'gimp_ui' as priority prefix for GimpUi introspected module.

Since meson 0.43.0 (below our current requirement), 'symbol_prefix'
argument of gnome.generate_gir() allows an ordered list. If I prepend
'gimp_ui', it makes any gimp_ui_*() function to not start with 'ui_'.

In particular, GimpUi.ui_init() becomes GimpUi.init() which is much less
redundant.

plug-ins/python/python-console/python-console.py

@@ -40,7 +40,7 @@ PROC_NAME = 'python-fu-console'
 RESPONSE_BROWSE, RESPONSE_CLEAR, RESPONSE_SAVE = range(3)
 
 def run(procedure, args, data):
-    GimpUi.ui_init ("python-console.py")
+    GimpUi.init ("python-console.py")
 
     namespace = {'__builtins__': __builtins__,
                  '__name__': '__main__', '__doc__': None,