Improve PhamePost search options

Summary: Ref T9360. This adds ability to search posts by blog(s) and by type better.

Test Plan:
Create some posts, search for them.

{F1705961}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T9360

Differential Revision: https://secure.phabricator.com/D16199