By using the FilteredTable, we get a quick-filter for all extending
parts for free. This includes:

- The Cross-platform page of the "Deployable features" export wizard.
- The Update Java Classpath page of the "Update classpath..." action
- The Template Selection page of the "Plug-in Project" page.

Together with the quick-filter comes a caching of the checked table
items. Those elements remain checked, even if currently hidden by the
filter and will be restored once they become visible again.