Implement input hints based on the active tool state (#388)

* Hook up user input hints to display in the frontend status bar

Closes #171

* MVP hint system based on tool FSM

* Fix hints for Fill and Eyedropper tools

* Add icons for keyboard shortcuts

* Fix hints for Pen Tool

* Cleanup

editor/src/tool/tools/navigate.rs

@@ -15,5 +15,6 @@ impl<'a> MessageHandler<ToolMessage, ToolActionHandlerData<'a>> for Navigate {
 	fn process_action(&mut self, action: ToolMessage, data: ToolActionHandlerData<'a>, responses: &mut VecDeque<Message>) {
 		todo!("{}::handle_input {:?} {:?} {:?} ", module_path!(), action, data, responses);
 	}
+
 	advertise_actions!();
 }