Draft: [feature] THORFi Lending

Implements THORFi lending.

Video walkthrough of the PR: https://www.youtube.com/watch?v=-V6GJu0TKbo

To enter lending use the following memo

colA = collateral asset (the pool you're taking a loan from)
units = number of LP units you're using as collateral
address = the address you want to receive the debt
targetA = the asset you wish to receive (ie BTC.BTC) (although THOR.USD is still used for accounting internally)
loan+:<colA>:<units>:<address>:<targetA>

To exit lending use the following memo. You can send in any asset, which gets swapped to THOR.USD and pays down the debt.

colA = the pool the loan is associated with
address = the loan owner
loan-:<colA>:<address>