Add Page Editor toolbar toggles and widen the default window

Edit mode, snap to grid and the widgets/properties pane are now toggles on
the main toolbar while the Page Editor is open. Outside edit mode the page
and the property sheet are read-only; drags snap to the 10px grid when
snapping is on. The default window grows by the right pane's width so the
canvas is not squeezed when the pane shows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app_state.py

@@ -8,7 +8,7 @@ so later rebinding would only ever be seen by the module that did it.
 import configparser
 import os
 
-VERSION = "0.0.0.130"
+VERSION = "0.0.0.131"
 PROPERTIES_FILE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "editor.properties")
 DEFAULT_GRID_SIZE = 10
 DEFAULT_ADD_TIMESTAMP = True