qt: add message field to SendCoinsRecipient

Also update URI parsing to fill in this field.
Note that the message is not currently used in any way with the client.
It should be stored with the transaction.

src/qt/guiutil.cpp

@@ -112,6 +112,11 @@ bool parseBitcoinURI(const QUrl &uri, SendCoinsRecipient *out)
             rv.label = i->second;
             fShouldReturnFalse = false;
         }
+        if (i->first == "message")
+        {
+            rv.message = i->second;
+            fShouldReturnFalse = false;
+        }
         else if (i->first == "amount")
         {
             if(!i->second.isEmpty())