Changes a contract job's pay/bill rates or adds lines (BF-7522).

Body: an array of { payBillItemId, costRate, billRate }. An item the job has gets the sent rates (a rate left out stays; all rows of the item change together); a new item is added with the company's flags and default or derived rates. Lines not listed are untouched; lines cannot be removed here. A line whose rate the company derives from another (for example overtime from regular) follows its parent unless the request sets it. Rates are 0 or more with at most 4 decimals. New rates apply to timecards generated after the change; existing timecards keep their rates and invoiced amounts never change.