ATX penalties/ATX incentives

[lrettig]

We want to incentivize smeshers to use a smaller number of larger identities, other things equal. One way to do this is to implement a per-ATX penalty, fee, or tax, based on the size/complexity of the ATX, to account for the cost to the network to transmit, store, and process that ATX.

For more see these research forum threads:

• ATX reward with a sliding window
• Non-trivial Improvements to PoST UX and large ATX incentivization (private)

See spacemeshos/go-spacemesh#4219