Wallet schema v2

* static table WalletV2 stores which send and receive methods a wallet supports
  => allows multiple send and recv methods per wallet
* split wallets by send and recv for easier validation of configuration instead of having both send and recv optional
  and rely on application logic to make sure the configuration is not invalid
* wallet method tables (WalletSend..., WalletRecv...) store configuration per user wallet
* use triggers to make sure that a method of a user wallet is actually supported by the wallet

How to add a new wallet:

* add a new row to the WalletV2 table and declare which send and recv methods it supports
* if it supports a new method, add a new method table to store the configuration

TODO:

* check if HTTP methods to send and recv (LNbits, Blink, Phoenixd) can be abstracted away via one WalletSendHTTP table without resorting to JSON columns

Author: ekzyis