Fix genesis bits and possibly other params

[nmarley]

Leaving this open as a TODO for now, one thing I've noticed is that the genesis bits value is set for Bitcoin, but not the Dash value: https://github.com/dashevo/dashcore-lib/blob/3a7f3c36ea62e495c137ead9e3013ea5a7aa103f/lib/block/blockheader.js#L12

Other things like our max block size are still legacy: https://github.com/dashevo/dashcore-lib/blob/master/lib/block/block.js#L30

Please keep this open and allow for a full review so that we can get them all at once, instead of just picking off those example values I described ^. I'd like to ensure we have a solid lib which includes all the necessary Dash params, adjusted appropriately from Bitcoin.

[SamKirby22]

Discussed on Triage - Alex, please retest and confirm if issue remains outstanding.

[dash-maverick]

Issue still outstanding - planned to be fixed but no high/urgent prio