Generate slightly shorter summaries in the typeahead browse dialog

Summary: Ref T11034. Try to produce a roughly-one-sentence summary instead of a roughly-one-paragraph summary for the browse dialog.

Test Plan:

• Added unit tests, ran unit tests.
• Wrote a longer summary for a project, browsed to it, saw a shorter summary.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11034

Differential Revision: https://secure.phabricator.com/D16892