Make device address an optional parameter

[ademcaliskan]

First of all thanks for the great work!

Some parts of the oled.js file need an update, if you want to use the module with new revs of the pi.

Rev.2 uses a different address -> dev/i2c-1

So I intend to make the device address as an optional paameter with /dev/i2c-0 as default, to preserve backward compatibility.

Thanks.

[roboflank]

:+1: