WIP for fixing WIP-0007 (or not) about data requests weight

[lrubiorod]

https://github.com/witnet/WIPs/blob/master/wip-0007.md

[mariocao]

The PR witnet/witnet-rust#1966 clarifies some of the DR weight formula parameters and removes a misplaced factor alpha. This PR does not change the logic as alpha=1. 😄

I will open a WIP with an amendment for the WIP-0007 in order to match the current implementation with what was specified.

DR_weight = DR_size*alpha + W*COMMIT + W*REVEAL*beta + TALLY*beta + (W+M)*OUTPUT_SIZE + N*INPUT_SIZE

While in the WIP-0007 join transactions were highly subsidised by the protocol, the implementation was taking into account the weight of the transaction inputs.

This could create a wrong incentive to create DRs with the only purpose of joining UTXOs and, therefore, reducing the remaining block bucket for legit DRs. Nevertheless, join transactions are still possible by using regular VTTs where inputs weight is much less compared to the outputs.