**NOTE: This contains a backwards incompatible database migration, so if you plan to test it, please make a copy of your database first.**
Moves tickets from a single database bucket containing JSON encoded strings, to a bucket for each ticket.
This change is to preemptively deal with scaling issues seen with databases containing tens of thousands of tickets.
This PR introduces a database migration which deletes any raw fee transactions which remain in the database after already having been confirmed on-chain. There is no need to keep these, and they take up a lot of space.
There is also a change in the background handler to ensure that in future, tx hex is always removed from the database when the tx is confirmed.
Plus a few other miscellaneous pieces which will be usedful soon:
- Remove `Get` from func names `GetCookieSecret` and `GetFeeXPub`.
- Add helpers to encode/decode integers/bytes.
* Remove unnecessary error handling.
* Generate fee addresses in dcrvsp, not dcrwallet
* Break loop if multiple invalid children are generated.
* Use Mutex instead of RWMutex
