Add spaces when rendering PhabricatorPropertyListView

Summary:
Ref T2319. In a property list view, if there's a property like:

  Property Name  propertyvalue

...and you double click "propertyvalue" to select it so you can copy paste it (maybe it's a branch name or a URI), you get "Namepropertyvalue" (or worse). Although this "fix" is hacky, it seems to work alright and not cause side effects.

Adding spaces between the tags instead (`<dt>x</dt> <dd>y</dd>`) did not work in Safari. Adding a `<span> </span>` between the tags did, but that seems even messier.

Test Plan: Double-clicked "propertyvalue".

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Maniphest Tasks: T2319

Differential Revision: https://secure.phabricator.com/D6026