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

I think this is the place to expose ideas and duscussion, thats fine. This is one kind of filter we can try to use, but detecting cycles in large networks can be expensive, as they can be arbitrarialy large… and banning intermediate addresses may not be effective if they have only small amounts of token, which is often the case. The stake idea is to guaratee attacks will hurt, and Im sure they wont happen anymore.