Preload images in Pholio and fix dimension rendering

Summary:
Preload all the images when viewing a pholio. Fixes T2692.

We should probably use lower-resolution previews on mobile and only show full resolution when the user taps. We should also suppress the thumbnails from loading on mobile since they aren't visible. But neither is critical for the moment.

Test Plan: Added logging, verified everything loaded.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2692

Differential Revision: https://secure.phabricator.com/D5316
Document icons sprite sheet.

Summary: Adds 32 and 64 px images to represent basic documents.

Test Plan: Differential

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5317
Apront Two Column View

Summary: Wanted to pull this out in case we don't use it in Maniphest, still useful perhaps in the future. Creates a sidebar that wraps when on mobile.

Test Plan: Tested UIExample

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5321
Minor, fix an extra period in Phriction.

Auditors: anhnhan