Burnup report showing decimals on hover

Summary:
Added yformat to ManiphestReportController. Removed [yy] from the js.
Will pull config.yformat or send []. The old way with [yy] never seemed to worked having config.yformat, also would crash if yformat was in with value

Test Plan: Loadup burn up report, hover over a given date. Number of tasks opened should be an int

Reviewers: epriestley, #blessed_reviewers

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8080