Fixes jsTree's relative URL construction for theme components

Calculates the path component of the URL used to load cms.changelist.js
and sets jsTree's settings.ui.theme_path relative to that.
Fix whitespace, remove '?' from script selector.

The '?' which was removed would cause the selector to only find the
<script> tag if cms.changelist.js had been specified with a query
string following it.
Merge pull request #2270 from jonprindiville/jstree-rel-marker-gif

Fixes jsTree's relative URL construction for theme components