Fixes a few loose ends in the full cycle of sending coins,
accepting them, pushing that transaction to the pool and having it
mined. More specifically:
* The API output endpoint needs to be a UTXO endpoint, as the
server can't make any guarantee about having a spent output.
* Bubbling up HTTP not found errors.
* Wallet output status checker now handles spent outputs.
* Transaction pool validates the transaction before accepting it.
* Fixed the operation API routes.
* Fixed too greedy wallet coin selection loop.
* Transactions coming from the network are now pushed to the pool
through the net adapter.
* New blocks accepted by the chain are sent to the pool for
eviction.
* The miner requests transactions from the pool to build its
blocks.
* The push API adds to the pool, removing the mock.
* Implementation of the adapter to the chain required by the pool
to get consistent UTXOs. Grossly unoptimized until we have the UTXO
MMR ready.