modify message type get value

[JoeCP17]

Hello, while I was looking at this project with interest, I modified the MessageType within the service method so that the item that retrieves the value through getValue can be returned directly from the AbstractMessage class, which is an abstract method.

Additionally, in the switch-case statement of convertToMessage, in addition to the value declared as the existing MessageType, I changed the part that was repeatedly declared as a string to use the value within the MessageType.

[markpollack]

I'm not super convinced on the change from getMessageType().getValue() to getMessageTypeValue() but I suppose it is a bit more readable so will merge it. The catch on using the string instead of the type is a good one!

Thanks

[markpollack]

merged as 5ff2c3b