Simplify ".device-phone X, .device-tablet X { ... }" rules
Summary: Add a ".device" rule which means "phone or tablet". Simplify about 5000 rules which were written ".device-phone X, device-tablet X { ... }".
Test Plan: Browsed the site a bit without incident.
Reviewers: chad
Reviewed By: chad
CC: aran
Maniphest Tasks: T1960
Differential Revision: https://secure.phabricator.com/D4103