speed enhancement, generic table access

[William la Forge]

I've added a prefiltering capability to the child table iterator. This is used in the table of users displayed for a user group. The idea is to filter out unwanted rolons BEFORE fetching them. Compatible with this is a qualifier pre-filter which filters out rolon which do not have a particular qualifier without fetching the rolon.

So how does it work? It works at the links level. We scan the links in the Children element, grab the UUID of each passing child, and then look in the qualifier's usage element for a matching link. This works best of course if the qualifier's usage element's btree is small enough to be cached.

I'll note that the table package in the AW4Servlets project is pretty generic. It should probably become its own module as it can support other UIs--not just the web UI.