Reduce Apps Sprite, Sidenav apps tweak

Summary: Removes lightblue app icons, moves the menu ones to menu sprite. Minor CSS updates to apps nav.

Test Plan: Test all sm icons work in new nav, test apps nav.

Reviewers: epriestley, btrahan

Subscribers: epriestley, Korvin, hach-que

Differential Revision: https://secure.phabricator.com/D9302