* Delay fee broadcast and adding tickets to wallets.
- Adds a `background` package which implements a dcrd notification handler. On each blockconnected notification, tickets with 6+ confirmations are marked confirmed, relevant fee transactions are broadcast, and any fees with 6+ confirmations have their tickets added to voting wallets.
- VSP fee is now an absolute value measured in DCR rather than a percentage. This simplifies the code and is more appropriate for an MVP. We can re-add percentage based fees later.
- Database code for tickets is now simplified to just "Insert/Update", rather than having functions for updating particular fields.
- Pay fee response no longer includes the fee tx hash, because we dont necessarily broadcast the fee tx straight away.
* Const for required confs
* Rework client/server authentication.
- Remove Signature from all requests, and instead expect a signature in HTTP header "VSP-Client-Signature".
- Remove CommitmentSignatures from the database.
- Use a bool flag to indicate when a ticket is missing from the database rather than an error.
This commit introduces a lot of duplication into each of the authenticated HTTP handlers. This should be removed in future work which moves the authentication to a dedicated middleware.
* Introduce auth and rpc middleware.
This removed the duplication added in the previous commit, and also removes the duplication of RPC client error handling.
