ArtNet-Server: use jspack to unpack the UDP Datagram

[iv-mexx]

Unpack UDP Datagram

The newest version of this module in npm is 0.1.0 where it seems that #7 has not been included so I started to fix this myself as well. Nevertheless, I feel that the use of jspack is a more robust solution than the previous fix.

Moreover, I was wondering if the Header should be checked and only be deserialised if everything is correct. Hence the todo in the code.

Also, I hav added a .gitignore to exclude the dependencies that are installed by npm and also to exclude some typical Windows and OSX files.