(Improvement) Throw on attempt to use recalc_price

[phahulin]

• What is it? (leave one option)
  • (Improvement) proposal (i.e. some existing feature can be improved)

It's best to explicitly avoid this part of code by throwing an exception, since it's not finished yet:

https://github.com/poanetwork/poa-popa/blob/e259cec1fcfcfdff30a52bffb395d845c774855b/web-dapp/server-lib/recalc_price.js#L20-L24