[Redesign] Clean up <select>

Summary: Ref T8099, Ref T8449. Adds a min width to selects (can't think of anything this breaks in ui) and adds space around space select.

Test Plan: Review a number of selects in different UIs, forms, dialogs.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8099, T8449

Differential Revision: https://secure.phabricator.com/D13523