Normalize button hints (#130)

## Summary

This creates a `renderer.drawButtonHints` to make all of the "hints"
over buttons to match the home screen.

## Additional Context

* Add any other information that might be helpful for the reviewer
(e.g., performance implications, potential risks, specific areas to
focus on).

---------

Co-authored-by: Dave Allie <dave@daveallie.com>

src/activities/network/NetworkModeSelectionActivity.cpp

@@ -122,7 +122,7 @@ void NetworkModeSelectionActivity::render() const {
   }
 
   // Draw help text at bottom
-  renderer.drawCenteredText(SMALL_FONT_ID, pageHeight - 30, "Press OK to select, BACK to cancel", true, REGULAR);
+  renderer.drawButtonHints(UI_FONT_ID, "« Back", "Select", "", "");
 
   renderer.displayBuffer();
 }