Refactor Payment PR 4

[ziggie1984]

• channeldb: rename PaymentControl struct
• channeldb: unify payment related code
• channeldb: rename pControl to paymentDB
• channeldb: fix linter
• lnd: introduce separate key-value payment db
• multi: unify all payment related kv data
• channeldb: add context to query method
• multi: add new payments package
• multi: fix linter
• multi: add new payments package.
• multi: move payment code from channeldb to payments lib.