Shutdown splash for the OLED script; restore non-Latin transliteration; other refactoring (#991)

- Bring back the shutdown splash, with the tweak that is blanks out after 700ms
- Restore the non-Latin transliteration originally from https://github.com/akuker/RASCSI/pull/449 which was lost when the `common` package was introduced
- Bump to the latest libraries, while removing implicit dependencies from requirements.txt
- Shorter duration of the startup splash
- Reintroduce shell shutdown/reboot methods for use with the Web UI. This addresses https://github.com/akuker/RASCSI/issues/538 (the ctrlboard client will continue to use the built-in rascsi system calls which are slightly faster)
- Remove overt references to RPi. This addresses https://github.com/akuker/RASCSI/issues/990
- Other refactorings

python/ctrlboard/src/ctrlboard_event_handler/ctrlboard_menu_update_event_handler.py

@@ -193,7 +193,7 @@ class CtrlBoardMenuUpdateEventHandler(Observer):
     # noinspection PyUnusedLocal
     def handle_action_menu_shutdown(self, info_object):
         """Method handles the rotary button press on 'Shutdown' in the action menu."""
-        self.ractl_cmd.shutdown_pi("system")
+        self.ractl_cmd.shutdown("system")
         self._menu_controller.show_message("Shutting down!", 150)
         self._menu_controller.segue(CtrlBoardMenuBuilder.SCSI_ID_MENU,
                                     transition_attributes=self._menu_renderer_config.

python/ctrlboard/src/ctrlboard_event_handler/rascsi_shutdown_cycler.py

@@ -19,7 +19,7 @@ class RascsiShutdownCycler(Cycler):
         if self.executed_once is False:
             self.executed_once = True
             self._menu_controller.show_timed_message("Shutting down...")
-            self.ractl_cmd.shutdown_pi("system")
+            self.ractl_cmd.shutdown("system")
             return "shutdown"
 
         return None