Use transactions to apply Ajax settings mutations

Summary:
Ref T4103. Some settings (mostly nav collapsed/expanded states) use this endpoint to make adjustments when users press keys (like \ to toggle the durable column).

All of these settings are now formal, so swap things over to transactions.

Test Plan: Collapsed/expanded various navs, reloaded pages, settings stuck.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4103

Differential Revision: https://secure.phabricator.com/D16035