Respect PM typing notification settings

[neiljp]

What does this PR do?

Tested?

• Manually
• Existing tests (adapted, if necessary)
• New tests added (for any new behavior)
• Passed linting & tests (each commit)

Commit flow

• Introduce & test new centralized user settings in model for new property (from register)
• Update the new property from events
• Use the updating property to determine whether to send typing events

Notes & Questions

This introduces user settings, which is intended as a new central location for this. This new setting is set and updated via user_settings, whereas older settings may be in multiple locations dependent on parameter passed to the server (user_settings_object)

I have initially assumed that this setting is only available in the new structure, but that's not completely clear to me.

Visual changes

For servers which support this setting, ZT currently shows warning notices in the footer, returned from the server. If requested via the setting, this PR avoids sending notifications, so the server doesn't send a notice, which then isn't shown.

[neiljp]

Merging this now after discussion in #api design > typing notification endpoint.