Use storage id + appframework for ext storage CRUD

- Added StorageConfig class to replace ugly arrays
- Implemented StorageService and StorageController for Global and User
  storages
- Async status checking for storages (from Xenopathic)
- Auto-generate id for external storage configs (not the same as
  storage_id)
- Refactor JS classes for external storage settings, this mostly
  moves/encapsulated existing global event handlers into the
  MountConfigListView class.
- Added some JS unit tests for the external storage UI