Add Spark Core board layout and automatic names to shortcut classes

@tino I added [spark core's layout](http://docs.spark.io/hardware/#spark-core-datasheet-pins-and-i-o) to `pyfirmata.boards.BOARDS` with a layout test.

I also made the shortcut classes set `self.name` automatically according to the board type after calling super on the `Board` base class since it can be useful in implementing board-specific functions later.