Maniphest CSS changes

Summary:

• Remove "0.5%" padding which makes Safari flip out and render every row differently sometimes.
• Remove list padding from ManiphestTaskListView, put it in the controller composition instead.

Test Plan: Viewed all places where task lists appear.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1788