Tweaked Holdings Maintenance so that it only shows the selected library, its ancestor...

Tweaked Holdings Maintenance so that it only shows the selected library, its ancestors, and its descendents, subject to a Limit menu for org depth (so for example, in the stock example hierarchy where you have Consortium -> System -> Branch -> Sub-Library/Bookmobile, if you Limit to Branch, you will not see any Bookmobile or Sub-Library orgs).  It no longer renders sibling libs when clicking through the list.

Also...

* some refactoring and comment removal
* less obtrusive but hopefully still useful menu entry styling for library entries that have volumes
* some defensive coding for util.make_menulist

git-svn-id: svn://svn.open-ils.org/ILS/trunk@17506 dcc99617-32d9-48b4-a31d-7c20da2025e4