Modernize user activity logs (ApplicationSearch, policies)

Summary:
Ref T4398. Ref T4842. I want to let users review their own account activity, partly as a general security measure and partly to make some of the multi-factor stuff easier to build and debug.

To support this, implement modern policies and application search.

I also removed the "old" and "new" columns from this output, since they had limited utility and revealed email addresses to administrators for some actions. We don't let administrators access email addresses from other UIs, and the value of doing so here seems very small.

Test Plan: Used interface to issue a bunch of queries against user logs, got reasonable/expected results.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: keir, epriestley

Maniphest Tasks: T4842, T4398

Differential Revision: https://secure.phabricator.com/D8856