Estimating and recording VRBO fees automatically

(So I don't need to do it manually) it would be nice for OR (for each API-integrated VRBO booking) to automatically estimate and record host listing fee.

Notes:

- can be made optional

- VRBO pricing is pretty much the same for most -- if not, configuration option can be added to augment behavior of "VRBO estimator" for given user/property

- it would play nice with earlier "Net Earnings" request

- doesn't have to be ideal -- if it is off by $10 no one would care. If you want to be super-precise with it -- introduce "contingent" flag which would be set for entries that are estimated. If given value was produced as result of calc with contingent value involved -- such value should be displayed differently