Switching between preview\edit overrides remote Markdown changes

### Expected
When markdown is disabled on other device, while Android app is in preview mode, app should either leave the preview mode (as in Electron), or forbid returning to it (iOS, macOS).

### Observed
It's possible to override Markdown enabled setting by going back to preview mode, because 'Preview' tab is not hidden.

### Reproduced
1. Android: Open any note and make sure Markdown is enabled
2. Android: Enter Preview mode
3. Other device: disable Markdown for this note
4. Android: go to Edit mode (note that 'Preview' tab is still there and Markdown is shown as enabled)
5. Android: Tap 'Preview' tab ~> Markdown is enabled again on remote device

Device Make: Samsung
Device Model: A31
Android Version: 10
Simplenote Version: 2.17-rc-1

No file, test, or entry point is named. Start by reproducing the Android steps and trace how the Preview tab and Markdown setting are refreshed after the remote device disables Markdown; done means Android no longer allows Preview to re-enable the remote Markdown setting.

Written by the indexing model from the issue text.