Added multiple skin support and better commandline parsing

Added multiple skin support and better commandline parsing
- Skins other than "classic" will be put into a subdir in the output directory (e.g. output/minimal/###.png)
- By default, "classic" and "minimal" badges are created for all players that were active in the last 6 hours
- A skin list can be passed to the program for testing (e.g. "gen_badges.py classic archer")
- The "-force" parameter enforces an update of all badges by setting delta to 2^24 hours
- The "-test" parameter limits the number of players to be considered to 200 (used for testing)