[neo-project/neo] Staked free tx [idea] (#357)

Guys, I’ve been wondering if a simple idea could work out to guarantee free or low fee tx, by providing the network a «guarantee» that staked address will «behave». The idea is add a «stake free tx» remark on a transfer, and after that, two things will happen:
1) address will apply for free/low fee (as long as amount is over StakeMinimumLimit of Neo or Gas)
2) if implemented filters catch transaction as «misbehavior», funds will be locked at this address for a given number of blocks

I believe this is simple and effective to prevent attacks while keeping fees low (or even zero). Another option is to use staked address signature on a different address to apply for low fees (while compromising the funds of the staked address). That may also have some applications, where funds are distributed, but staked funds are in a centralized point.