drep_voting_power_history: needs rewrite to be more performant across networks

[hodlonaut]

Also, currently it allows for both epoch_no and drep_id parameters to both be absent, which in turn tries to extract 1000+ Dreps x 100s of epochs of data - we should make it so if epoch_no is not specified, then current epoch is used by default. Any user that wants historic data can obtain it once off and store it on client side for future use, etc.