* Calculate fee from percentage.
- Reverted config to accept a fee percentage, not absolute value.
- The fee amount to be paid is now included in the `getfeeaddress` response. The current best block is used to calculate the fee percentage, and new blocks may be mined before the fee is paid, so the fee expiry period is shortened from 24 hours to 1 hour to mitigate this.
- Rename ticket db field to FeeAmount so it is more representative of the data it holds.
- API fields renamed to "FeePercentage" and "FeeAmount"
- Relay fee is still hard coded.
* Use getbestblockhash
* 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
