Extend the representative-item logic to handle ingredients specified
as the intersection of multiple groups. Also add mangling of item
button content, because comma for a multi-group ingredient is getting
formspec-escaped and then not de-escaped.
When the current search produces no results, give a specific message
rather than "Page 1 of 0". Don't display the "Filter:" label if no
filtering is currently applied.
Keep the current inventory search string when performing inventory
form actions other than searching. This means the player's input is
not lost if the player breaks off from entering it to switch pages,
or if the player absent-mindedly ends text input with <return>.
