This patch adds a painting delegate to the icon column of CommandPalette
to show a radio button in case an action is checkable and does not
explicitly have an icon :^)
You can now press Ctrl+Shift+A in any LibGUI application and we'll give
you a command palette dialog where you can search for context-relevant
actions by name (via the keyboard.)
The set of actions is currently the same one you'd access via keyboard
shortcuts. In the future, we'll probably want to add APIs to allow
richer integrations with this feature.
