Fixes for exchange address implementation

[psolstice]

PR intention

This PR solves the following issues:

• outputs of transactions sending funds to exchange addresses are treated as change
• listtransactions doesn't output exchange address txes
• gettransaction can't parse exchange address
• coin control dialog shows exchange addresses in incorrect group
• incorrect prefix for testnet's exchange address

Code changes brief

getnewexchangeaddress now properly adds generated address to the wallet's address book