allow option to explitly opt into mutli tx fee

[eonwarped]

If the parameter is enabled, throw an error if the he__burnFee parameter is not set on a transaction where we are expecting a fee to be paid.

[AlexTrapp]

This error is essential for the new fee to be "real and official".

Many tx types still do not require a fee (and I think this is good and fine, these types are not "spamming" currently.) We should look to fix the arbitrary 50 limit to 500 nft per tx, and then a multi tx fee could apply there too.

But anyway you look at it, and at any time in the development path - if its going to error - it must throw an error so people "know" whats happening.