Clean up UITooltips

Summary: Fixes positioning issues by creating another container to hold the abs. positioned arrows. (Issues primarily presented on Workboards).

Test Plan: Test UI arrows on a workboard, applciation launcher, and in UIExamples.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D10897