Don't show notifications about your own actions

Summary:
Ref T6559. See discussion in D11143. At least locally, WebSockets are too fast and create immediate local notifications on page submit.

To mitigate this, don't notify about your own actions.

This isn't perfect (we get the other-copies-of-the-window-open-in-other-tabs case wrong) but I think the case we get wrong is rare / not very important.

Test Plan: Submitted stuff, saw other users get notifications but not me.

Reviewers: btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T6559

Differential Revision: https://secure.phabricator.com/D11275