Tests for update settings endpoint

[nicole-mcg]

Some tests should be created for the update settings endpoint. This endpoint should also be changed to give a response indicating whether it was successful.

This will require setting the Account.directory variable for each test (See documentation in file_server/web/account.py)

Tests:

• Verify settings property returns Account.DEFAULT_SETTINGS on a new account, and verify _settings property on account is an empty dict.
• Set properties using endpoint and make sure all expected properties are there (and no extras). Verify settings and _settings properties are correct. Reload account using Account.load_account and verify those properties again
• Try to set properties not in Account.DEFAULT_PROPERTIES and verify they aren't added