Improve PhabricatorObjectItemListView handling of wide content

Summary: Wide content is currently allowed to push too far to the right, overlapping icons. Prevent it from doing so.

Test Plan:
Before:

{F27906}

After:

{F27907}

After, Mobile:

{F27908}

Reviewers: chad, codeblock, btrahan

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D4212