Prepare 0.9.0

Fix PaymentDepot#total_tax_sent and #total_owner_sent

Add payment depot filterer for use in the API

Update changelog

Serialize PaymentDepot three more fields; add forwarding_transaction_fee

Set field to test that a string is returned

Serialize PaymentDepot#min_payment

Prepare 0.8.4

Fix use of `send_many`

Follow the `check_limit`

Use `Blockchain::Address.transactions` and not `.txs`

Check payment_depots whose `checked_at` is nil as well

Prepare 0.8.0

Only fetch latest block if needed

Ensure that only payment depots that ought to be checked are checked