This allows both tspend and treasury policies to be set by clients on a per-ticket basis. Preferences can be set when initially registering a ticket with `/payfee`, and can be later updated using `/setvotechoices`.
Any requests which alter treasury/tspend policy will be stored in the database using the existing accountability system.
**Note:** This does not include consistency checking, it will need to be added later when dcrwallet has an RPC to retrieve policies in batches.
- Fee tx status is now tracked using a dedicated field, with values none/received/broadcast/confirmed/error.
- Fee tx hex and hash are now both set in /payfee. The absense of txhash is no longer used to determine if a fee tx has been broadcast or not.
- setvotechoices can no longer be called before a fee is received.
- Remove `binding:required` from response types. It has no effect on responses, it is only needed on request types which are validated by gin.
* 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.
