Add BaseFee on genesis block for dev.pow chain

[ziogaschr]

This fixes mining (panic), when --dev.pow flag is being used, by setting the BaseFee on the genesis block.

[meowsbits]

Checked locally, fixes it for me.
Note that it will NOT work if you re-run on top of a failing database version from master; you need to remove and replace the datadir (or at least the genesis block entry).
The --dev.pow program runs by default with only an in-mem db, so this is an edge case.

[ziogaschr]

Indeed, but because datadir has to be set to persist the DB and also that --dev.pow is a newer addition, I though of not trying to fix existing chains.
What do you think of that?