Filters in the item configuration list

There are a couple of usability problems with the item filters:

1. When you open the list of item for a host it sets the "Host" filter. If you press "Reset" it clears all filters, including "Host". Then, when you press "Filter" it doesn't display any items. The "Reset" button should probably reset the "Host" filter to the default value, not clear it.

2. When a subfilter contains no items, it becomes gray, but is still clickable. It shouldn't be clickable.