*.sok format support

[ezze]

Support *.sok levels' sets format:

http://www.sokobano.de/wiki/index.php?title=Sok_format

Also try to load them from a local computer: http://www.html5rocks.com/en/tutorials/file/dndfiles/

[ezze]

Simplest SOK loader is implemented: 78a30d4

It doesn't read meta data yet but all 12 Sasquatch level sets are playable now. :)

[ezze]

Loading local level sets is implemented.