Improve text overflow behavior for hovercards with (for example) long package names

Summary: See PHI977. Ref T13216. Some text, like long package names, may overflow hovercards. Add overflow CSS behaviors to remedy this.

Test Plan:
Before:

{F6012699}

After:

{F6012700}

(You can use /search/hovercard/ to render hovercards in a handy standalone way.)

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13216

Differential Revision: https://secure.phabricator.com/D19809