Render hashtags as colored/icon'd project tags

Summary: In most cases we preserve what the user typed, but showing colors/icons/names is more useful than #yolo (and makes aliases more usable without loss of meaning).

Test Plan: {F174510}

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D9831