Add exFAT support (#150)

## Summary

* Swap to updated SDCardManager which uses SdFat
* Add exFAT support
  * Swap to using FsFile everywhere
* Use newly exposed `SdMan` macro to get to static instance of
SDCardManager
* Move a bunch of FsHelpers up to SDCardManager

src/activities/settings/SettingsActivity.cpp

@@ -1,9 +1,9 @@
 #include "SettingsActivity.h"
 
 #include <GfxRenderer.h>
-#include <InputManager.h>
 
 #include "CrossPointSettings.h"
+#include "MappedInputManager.h"
 #include "OtaUpdateActivity.h"
 #include "config.h"