Layout shield on Arduino PCB footprint

The shield is currently laid out on a custom PCB footprint and lacks mounting holes that may be used to secure the board in a case as well as making sure the electrical connections are stable. Laying out the shield's components on a copy of the Arduino PCB footprint would take care of current limitations while ensuring alignment of the shield on top of the Arduino board and facilitating the use of mechanical fasteners such as standoffs and screws.

Will also solve https://bugs.launchpad.net/meadl/+bug/683213