* major types cleanup, more formatted api methods onto new request method
- getPaymentChannel() now uses this.request()
- getSettings() now uses this.request()
- getLedger() now uses this.request()
- transaction types cleaned up a bit, but still some work left to do
* Add request interface & typings
- src/api: add basic implementation of request/requestAll()
- src/ledgers/account_info: refactor to simplify with request()
- src/ledgers/balances: refactor to simplify with request()
- src/ledgers/orderbook: refactor to simplify with requestAll()
- src/ledgers/orders: refactor to simplify with requestAll()
- src/ledgers/trustlines: refactor to simplify with requestAll()
* standardize on Formatted prefix