Notify of fees on sign raw transaction

[jdogresorg]

When signing a raw transaction, we should notify / confirm action with user before broadcasting tx.

Notify user of the following :

• BTC Miners fee
• Data encoding costs
• Total amount being spent in tx = (sum(input.value) - miner_fee)

[jdogresorg]

coded up a BTNS decoder, which also decodes counterparty transactions into the raw data...

https://github.com/jdogresorg/BTNS-Decoder

Use this library to decode what the transaction is trying to do and confirm it with the user.

[jdogresorg]

Partially addressed by commit 4febac6 by decoding any XCP data and confirming with user.