Fix an issue with rendering PHID lists containing `null` in Maniphest

Summary: See IRC. Someone got a `null` in CCPHIDs somehow. Moving to subscriptions should prevent this, but paper over it for now.

Test Plan: Will have @dctrwatson check.

Reviewers: btrahan, dctrwatson

Reviewed By: btrahan

CC: dctrwatson, aran

Differential Revision: https://secure.phabricator.com/D7330
Misc Diffusion/Differential CSS tweaks

Summary: Various tweaks and fixes. Adds a File Contents view in Diffusion, normalizes spaces, colors.

Test Plan: tested differential and diffusion in my sandbox.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T3952

Differential Revision: https://secure.phabricator.com/D7325
Delete unintentional phlog()

Leaked in D7329.
Phtize phabricator-remarkup-assist

Test Plan: Translated 'bold text' as 'txt', clicked on B without selection, saw 'txt'.

CC: epriestley, aran

Differential Revision: https://secure.phabricator.com/D7335
Implement Graphviz, Figlet and Cowsay as Remarkup interpreter blocks

Summary: Fixes T3274. Fixes T3964. Ref T3591.

Test Plan: {F70928}

Reviewers: btrahan

Reviewed By: btrahan

CC: chad, aran

Maniphest Tasks: T3274, T3964, T3591

Differential Revision: https://secure.phabricator.com/D7332