Update pi4j and address api changes

[ConnorWhalen]

We have to update pi4j to fix #328. Doing so has broken some of our code, mostly catching new exceptions when using serial.

@cal-pratt check the changes to MaestroChannel closely because I might have screwed up your byte management. serial.read() returns a byte array instead of a char now.

[cal-pratt]

On second thought, the byte reads don't even matter because we don't use the voltage or current sensor