Allow word wrapping differential revision property labels

Summary:
Because D1028 caused the column containing differential revision property
labels to have a fixed width, some custom labels are longer than what fits
(and it makes more sense to word wrap them instead of making the column
wider).
I also updated the corresponding maniphest css for consistency.

Test Plan:
Used firebug to remove css property and visually check that is the intended
effect; loaded a page after the revision and saw that the css property is
no longer set, allowing the labels to wrap.

Reviewers: epriestley, jungejason

Reviewed By: jungejason

CC: aran, jungejason, epriestley

Differential Revision: 1066