Handle call notification the same way than other notifications.

Display the call notifications in the Notification app, with buttons to accept/reject the call.

src/displayapp/screens/Tile.h

@@ -29,8 +29,6 @@ namespace Pinetime {
           lv_obj_t * btnm1;
           bool running = true;
 
-          std::unique_ptr<Modal> modal;
-
           const char* btnm_map1[8];
           Pinetime::Applications::Apps apps[6];
       };