Improve options to sort and filter results

Both in product tracker and database: * Remember last sort setting. Default seems to be "last added" while most sellers will have a preference to sort on "sales" or "turnover". * Extend sorting options with EAN and Price * Turns columns into filters, especially the column Categories in the product tracker. If your tracking list is long it's not easy to eg filter all non-categorized items or items with two categories attached.