Disable notifications for your own actions

Summary:
Actions you made no longer show up in the lighting-bolt
dropdown. I didn't touch realtime notifications but they're transient
enough that it shouldn't matter too much?

I wonder, though, whether it would be more useful to have the
notifications still present but automatically marked read.

Test Plan:
Create notifications; muck around in the database; check that
the dropdown and list pages are displaying correctly.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T1402

Differential Revision: https://secure.phabricator.com/D3360