[refactoring][#1] split the baseline recsystem in a RenewalRecsystem baseclass

the base class implements the low-level (e.g. websocket client) functionality,
a basic CLI, basic RPC methods (actually just 'ping' for the moment)

the BaselineRecsystem need only implement the initialize() method and the
remaining RPC methods, as well as slightly extend main() to add the --mode
option

contestants may either subclass RenewalRecsystem to start with bare functionality
and build up from scratch, though they may be able to get started quicker by
subclassing BaselineRecsystem and modifying it (especially the recommend() method)
with their algorithms