Make icons in tags more floaty, less absoluty

Summary: This change wraps the icon inline with the text, so smaller width icons have equal spacing between the border and text.

Test Plan:
review a number of different tag with icons, also UIExamples.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11802