Added functionality for 2 different players

- You can now pass 2 different usercode files for two players.
- Running the simulation will actually update the field and robots! (so
you can actually run a game)

You can now actually run the game with 2 real bots, not just 1 bot and 1 dummy.
Also, you running a turn will cause the game to update, along with the field and bots, so if a bot attacks another bot, that bot will actually lose health, etc.

How to pass a second bot:
rgsimulator.py -u secondbot.py firstbot.py

Existing usages still work:
rgsimulator.py firstbot.py