SD card support

This adds SD card support to:

1. st3m, providing st3m_fs_sd_* functions and automatically attempting to probe the SD card on st3m_fs_init().
2. Recovery mode, providing SD card Disk Mode
3. The main firmware, attempting to mount the card to /sd on startup.

python_payload/st3m/ui/menu.py

@@ -100,7 +100,6 @@ class MenuItemBack(MenuItem):
         ctx.text("\ue5c4")
 
 
-
 class MenuController(ViewWithInputState):
     """
     Base class for menus. Reacts to canonical inputs (left shoulder button) to