Fix ItemSetChange issue in FiltertableListContainer

Filters need to be re-applied when the parent ListContainer fires an
ItemSetChange.
Note that this change also requires some defensive coding in
FilterableListContainer as it will not yet be fully initialized when the
first call to fireItemSetChange comes in from ListContainer.
Merge pull request #7 from jdryan1/fix_itemsetchange_issue

Fix ItemSetChange issue in FiltertableListContainer