Previosuly there was the problem that the state was saved when the
bot object was destructed.
When there was an unhandled exception it was possible for the builtins
to be cleanedup before the bot's destructor was executed resulting
in yet another exception because the open builtin was no longer
available.

This is no longer possible when the bot is used as a context manager
python guarantees that the __exit__ code is executed before leaving
the with block.

This allows us prevent the state from beeing saved when there was an
exception to prevent invalid states.

This makes the class more flexible and allows for different means of
sending the replies back by executing a subprocess or using dbus/jsonrpc.

Also remove the never used group send command.

Make the Geldschieberbot constructor parameters mandatory and let the
caller handle the configuration.

Previously the geldschieberbot module used global variables retrieved
from the environment for its configuration.

This is not very flexible and can lead to problems when using the module
from other python code. Therefore make all configuration Geldschieberbot
specific and pass the values to the constructor.

If no values are provided fallback to the environment.
This change is fully backwards compatible.