BV: limits on KETH that a authority node can hold

[david-sg]

Motivation:
To limit the potential damage from a hack to one of the authority nodes, check for the account balance of the node and if >= 10000, sweep 5000 to another account.

[jdetychey]

Good one.
Authority nodes could also have an auto-burn script.
if balance >= 10000 send 5000 to 0x0000