Added sample agent + log file writing/parsing

Added sample agent + log file writing/parsing

I figured no one wants to sift through the qchess internal agent stuff,
So I wrote a python external agent agents/sample.py

I ended up implementing the cool idea about log files.
You can replay a log file up to an arbitrary point, and then continue play.

I also fixed a bug with external agents calling run_agent.
Removed the reading of the colour line from there, since the external agent should do it.
Added reading of the colour line to the ExternalWrapper class, to avoid breaking that.

Added --reveal so that all states can be seen in the GUI (but they are not communicated to Agents).

Added handling of SIGINT to main.py

Probably did something else I forgot.

qchess will probably be ready soon (famous last words), I should start on a scoring/entry system...
And a webpage.