[Qt] Show and store message of normal bitcoin:URI

bitcoin:mrhz5ZgSF3C1BSdyCKt3gEdhKoRL5BNfJV?amount=0.0001&label=Donation&message=Thank%20you!

Message is shown in sendcoinsdialog and transaction details. Stored in walletTx->vOrderForm.

![message1](https://f.cloud.github.com/assets/2814559/1969649/3f5afb70-82f6-11e3-9db4-cb6b61d14fcd.png)

![message2](https://f.cloud.github.com/assets/2814559/1969651/4566dd72-82f6-11e3-82ee-65df1bbdf6da.png)