Summary:
- Handle the possibility that any access to localStorage causes error.
- Move getStorage() and getSessionStorage() safe functions to a separate file.
- Use these safe functions in more places.
Test Plan:
Added a test case, using a webdriver instance that blocks third-party cookies,
to enforce third-party restrictions. Added to gristUtil a way to override the
webdriver instance.
Reviewers: jarek
Reviewed By: jarek
Differential Revision: https://phab.getgrist.com/D3719
