Dpos storage size

[mfrankovi]

On a mainnet instance state_db takes almost as much space as the standard db. Inside of it over 90% of storage is taken by the validators storage which is increased on every block when rewards are distributed. Investigate if there is a way to optimize this to reduce the size.

[kstdl]

In this task I also checked why splitting one DPOS contract object into two requires a lot more space(I expected some raise, but not so big). And the thing is that we are saving data by some hash in data, and adding this hash to MPT, so we can find data. So I believe a lot of optimizations could be done there