Fix global variables

[svenpruefer]

Find a good solution for global variables for the AIs in order to preserve some knowledge for after an AI run.

In Mathecamp 2017, some players used globals() or similar hacks. It might be better and easier for new python developers to just predefine a list variablesToKeep which they can append as they wish.

Also, we could make that list non-empty by default and this way have an easy interface for the AIs to give some information to the main program. For example this could be individual player seekers names to display, some debugging data, a message to the fans or a war cry of a seeker right before it is hitting an enemy seeker :-)