R1:e9804bb7e5f1

Provide hovercards for generic edge stories, and include more message information in commit hovercards

Summary:
Ref T13620.

- Make generic edge stories render links with hovercards. Other story types (like subscriptions) already do this so I'm fairly certain this is just old code from before hovercards.
- Include a longer commit message snippet in hovercards.

Test Plan: {F8465645}

Maniphest Tasks: T13620

Differential Revision: https://secure.phabricator.com/D21574