Replace Roboto Slab with Aleo for PHUIDocumentView

Summary: These fonts are functionally very similar, but in diagnosing a problem with mobile Safari/Chrome, it turned out that our use of "bold" with the "normal" font build created a "semibold" look when on desktop and a "normal" look on mobile. The "semibold" feel is more important, so finding a lighter "bold" font was the impetus for this font switch. As it turns out Aleo is built by the same author as Lato (our other font) and is intended as it's companion. So stylistically, this is the more correct font.

Test Plan:
Test Phriction, Legalpad, Diviner, Desktop and Mobile

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14391