Fix QFN44-1EP

The 7x7 package was not fitting at all. Fixed the pad position and the silkscreen accordingly. Furthermore I added thermal vias to the centre pad. I hope that adding thermal vias to modules is compatible with the kicad-way. For me as a designer this would be quiet handy.

Designed for and tested with atmel atxmega128a4u.

Thx Carl :)