Fix cursor blinking problem

The problem was that when the editor had no events the cursor was not
blinking because the event loop was blocking on wait_event.

Now we no longer calls wait_event without a timeout if the windows has
the focus. When the window has the focus the timeout is set to 1 / fps
so that the cursor can blinks.

In addition we react to the "focus lost" event to ensure the documents
are redrawn without the cursor.

data/core/rootview.lua

@@ -504,6 +504,11 @@ function RootView:on_text_input(...)
 end
 
 
+function RootView:on_focus_lost(...)
+  -- We force a redraw so documents can redraw without the cursor.
+  core.redraw = true
+end
+
 function RootView:update()
   copy_position_and_size(self.root_node, self)
   self.root_node:update()