Limit width of differential, maniphest properties tables

Summary:
Sometimes, elements in a property table at the top of a differential
revision view or maniphest task detail view will have a minimum width
that is too wide to fit in the table without causing the table's width
to exceed the width of its parent div. This diff changes the table layout
algorithm so that the table's width never exceeds the width of its parent
div. In the case of a code block causing the excess width, it puts a
scrollbar on the block instead of letting content spill out.

Due to the way the fixed table layout algorithm works, the width of the
left column (containing headers) is set to a fixed width. I chose a width
for differential that works with the default headers, but site-specific
headers might not fit.

Test Plan:
Created a task, added a code block in the description that had an
unreasonably long line in it, and visually verified that the <td>
containing the <code> did not expand horizontally past the limit defined
by the <div> containing the <table>. I also loaded a differential revision
view and checked that its table looks sane.

Reviewers: epriestley, jungejason, aran

Reviewed By: epriestley

CC: aran, nh, epriestley

Differential Revision: 1028