BUG: Users can modify settings during a sync if the Features or Settings page was already open

[JakePT]

Describe the bug
Normally during a full delete and sync the Features and Settings pages are disabled to prevent changing settings, enabling or disabling features, or modifying feature settings during this process. However if the use opens the either page in before syncing, and keeps it open while starting a delete and sync in another tab, they will be able to make those changes while the sync is occurring.

Steps to Reproduce

1. Open the Sync page.
2. Press Delete all Data and Start a Fresh Sync.
3. While this is happening open the Features page in the same tab. It should be greyed out and disabled.
4. Once finished, open the Sync page again.
5. Then open the Features page in a new tab.
6. Switch back to the Sync page and press Delete all Data and Start a Fresh Sync.
7. While it is syncing switch to the other tab with the Features page open. It won't be disabled and it will be possible to modify and save settings.

Repeat for the Settings page. The behaviour will be the same.

Expected behaviour
Saving Feature settings while a sync is occurring should fail, and an error message displayed. Ideally at this time the relevant page should become disabled to match its behaviour when it's opened during a sync.