Track investments/redemptions in onchain cash asset

[hieronx]

When an epoch is executed, this should create

• If total investments > 0, an AssetTransaction with type=DepositFromInvestments for asset ID = 0 (onchain cash)
• If total redemptions > 0, an AssetTransaction with type=WithdrawalForRedemptions for asset ID = 0 (onchain cash)
• If total fees paid > 0, an AssetTransaction with type=WithdrawalForFees for asset ID = 0 (onchain cash)