Add support for Qt backend

[dimitry-ishenko]

Currently firmata::io::serial is implemented using the Asio library. However, for GUI apps using Qt it would be nice if there was a native Qt implementation using QSerialPort.

Plan of attack:

1. Create abstract/interface serial class.
2. Modify existing serial class as an implementation of (1).
3. Add serial class implementing (1) using QSerialPort.