Have form elements default to the standard font size.

Summary: Font size globally is 13px, but form elements were 12px and harder to read. This helps readability and consistency with form elements.

Test Plan: Checked various forms, left comments.

Reviewers: epriestley, btrahan

Reviewed By: btrahan

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4377