Show zero-balance / fully-paid orders on Open Balances (toggle)

Open Balances currently only shows orders with money still due. Add a toggle 'Show all customers (including zero balances)' so the page works as a master customer report, not just an outstanding-receivables list. Quote: "If I could get [Open Balances] to just show everything, zero balances and everything, it might be that that's all I need." Source: Martin / Indianola Memorial Works phone call.