Add some spacing around jx-tooltips

Summary: Using tooltips with icons is problematic because we currently draw the arrow after the tooltip location, meaning it goes 5px into the container. This gives a 5px padding around the outer container to better account for this.

Test Plan: tested tooltips in remarkup bar, project icon nav, and in durable column.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12184