Log miner fee (#237)

* Get miner fee written in some wallet plugins

* Return txid and fee for geth. possible problem with txid (zero hash on pending transaction)

* bitgo fee return

* Wallet apis fees save in cryptoAtoms

lib/plugins/wallet/mock-wallet/mock-wallet.js

@@ -51,7 +51,7 @@ function sendCoins (account, toAddress, cryptoAtoms, cryptoCode) {
 
       console.log('[%s] DEBUG: Mock wallet sending %s cryptoAtoms to %s',
         cryptoCode, cryptoAtoms.toString(), toAddress)
-      return resolve('<txHash>')
+      return resolve({ txid: '<txHash>', fee: BN(0) })
     }, 2000)
   })
 }