[web/css] move jquery.treeview.css override to a separate file
Patched embedded code copies are a maintenance disaster (even more so
than plain embedded code copies). Let's not do that.
[web] Stop patching jquery.treeview.js
This logically reverts part of e9b7cd2e9012 "allow treeview to work
correctly in a tab #345293".
The treeview and ajax code have suffered a number of changes since then, this
change doesn't seem to be necessary anymore. It is most likely unneeded since
f65208c9dbdc "[javascript] use jQuery.one('ajax-loaded') instead of
jQuery.bind() in add_onload to avoid multiple callback executions".