fac0db0 wallet: Make fee settings non-static members (MarcoFalke)
Pull request description:
The wallet header defined some globals (they were called "settings"), that should be class members instead.
This commit is hopefully only refactoring, apart from a multiwallet bugfix: Calling the rpc `settxfee` for one wallet, would set (and change) the fee rate for all loaded wallets. (See added test case)
Tree-SHA512: 4ab6ec2f5c714742396ded5e451ec3b1ceb771e3696492de29889d866de4365b3fbe4a2784d085c8b8bd11b1ebb8a1fec99ab2c62eee716791cfc67c0cf29e1b