[SP] Automated Swap Backend

[D4nte]

The Service Provider (SP) also runs a backend that has the role to execute swaps. The backend...

• Nectar #174 WIP - automatically executes a swap when reached via the p2p interface.
• gets any related configuration items for a config file, the config file has reasonable defaults.
• provides an API to allow the website to access the current rate.
• uses kraken mid-market rate as rate.
• uses an up-to-date rate when locking the Bitcoin asset.
• does not proceed with swap execution if predicted Bitcoin quantity to sell is above a configurable ratio of total balance.
• uses bitcoind wallet as Bitcoin Wallet.
• uses monero-wallet-rpc as Monero Wallet.
• prints Bitcoin cancellation, Bitcoin punishment transactions when computed
• prints Monero (refund) private key when the protocol allows (Bitcoin refunded)
• can run several swaps concurrently.
• Bonus: bundles the swap website, allowing the SP operator to just proxy from their favourite webserver.

[da-kami]

Notes on can run swaps concurrently, after working on #147 I see the following issues to be resolved to make concurrent swaps happen (given the code base at the time):

• Separate EventLoop and EventLoopHandle - I think we will need this to make concurrent swaps possible. We should be able to drive a swap through a handle without creating a new EventLoop. I think the EventLoop should live in the factory, while the handles live in each swap. (Currently the EventLoop is returned upon creating a swap.)
• Don't just have one swap_id in the Factory but have a list of swaps.
• Make swaps identifiable in the network communication.

Recording this here so I can get it out of my head for now.

[D4nte]

Regarding can run swaps concurrently, it also means concurrent access to the DB. I think we should do #133 to not end up fixing the db concurrent access twice.

[thomaseizinger]

Closing because epic from previous project.