Split Balancer OHM-DAI-ETH pool into OHM-DAI and OHM-ETH pools

The upcoming automated RBS system will require 2 asset pools for automatic LP rebalancing. In preparation for this, the current 3 asset pool needs to split. After discussion on October 28 it is proposed that the pool is split before the RBS launch to avoid disruptive liquidity changes at a later stage.

Proposal Split Balancer OHM-DAI-ETH pool into Balancer 50/50 OHM-DAI and 50/50 OHM-ETH pools. Do the change in two steps by migrating half of the OHM-DAI-ETH pool first, then the rest.

Also migrate the AURA pool.