add ability to move from normal mode to move mode, and from move mode back to normal mode

fcore/normal-mode.sml

@@ -336,6 +336,11 @@ struct
       (model, fileMsg)
     end
 
+  fun enterMoveMode model =
+    let val model = AppWith.mode (model, AppType.MOVE_MODE)
+    in (model, [])
+    end
+
   fun handleFileBrowserAndPathInNormalMode (model, fileBrowser, path) =
     let val model = AppWith.fileBrowserAndPath (model, fileBrowser, path)
     in (model, [])
@@ -356,6 +361,7 @@ struct
     | KEY_A => updateAlpha model
     | KEY_W => updateCanvasWidth model
     | KEY_H => updateCanvasHeight model
+    | KEY_M => enterMoveMode model
     | RESIZE_WINDOW {width, height} => resizeWindow (model, width, height)
     | UNDO_ACTION => undoAction model
     | REDO_ACTION => redoAction model
@@ -377,4 +383,5 @@ struct
     | KEY_SPACE => enterOrSpaceCoordinates model
     | FILE_BROWSER_AND_PATH {fileBrowser, path} =>
         handleFileBrowserAndPathInNormalMode (model, fileBrowser, path)
+    | KEY_ESC => (model, [])
 end