Add obstacles and actions modules

We need these modules both in the server and client code. Even more
important, we need these in the driver code, and we certainly do not
want to have ugly imports in the kids code.

Although the modules are minimalistic (specially the actions module),
this allows nice code as:

    from common import actions
Remove unused file

gameServer.py was never used.
Move all configuration to common config

We have server configuration, client configuration, and common
configuration. The simplest solution is one config file in the common
directory.

While moving the configuration from matrix_config, all names renamed to
lowercase. Configuration is *not* constants, which do not change.
Rename matrix module to track

Racing is done on a racing track, not on matrix. The old name was
specially silly when accessed self.matrix.matrix. This read better, now
as self.track.matrix.