Workboards - remove 7 column restriction

Summary: Fixes T4914. We currently have a finite limit on column displays which caused T4914. This fixes T4914 by no longer using a fluid layout. Rather, we use a fixed column width layout which does not have a 7 column limit. Future work - see T4054 for an example - will likely make the fluid layout thing work with infinite columns, and / or other work may re-jigger project workboards directly.

Test Plan: had a project like in T4914 that wouldn't load and it loaded post this change! added more columns and using javascript inspector noted proper width being set

Reviewers: epriestley, chad

Reviewed By: epriestley

Subscribers: joshuaspence, epriestley, Korvin

Maniphest Tasks: T4054, T4914

Differential Revision: https://secure.phabricator.com/D8942