* Addded support for private storage.
Include 'private' flag parameters to the Store class and save_json function.
Updated various authentication and onboarding classes to use private stores.
Fixed unit test for emulated_hue which used a mock patch on save_json().
* Fixed Hound formatting issues not detected by local linting.
## Description:
Make typing checks more strict: add `--strict-optional` flag that forbids implicit None return type. This flag will become default in the next version of mypy (0.600)
Add `homeassistant/util/` to checked dirs.
## Checklist:
- [x] The code change is tested and works locally.
- [x] Local tests pass with `tox`. **Your PR cannot be merged unless tests pass**
* Add storage helper
* Migrate config entries to use the storage helper
* Make sure tests do not do I/O
* Lint
* Add versions to stored data
* Add more instance variables
* Make migrator load config if nothing to migrate
* Address comments
Nicko van Someren
Ville Skyttä
Paulus Schoutsen
Andrey