lcm/lcmgl integration with simulate then playback


Resolves issue #223 by implementing the first idea:

I could add a block, which would operate much like the realtime block (e.g. no, inputs, no outputs), which can be stuck into the simulink diagram during simulate if, say, options.capture_lcm = 'lcmgl.*'. That block will simply subscribe to the specified channels, and record all of the lcm traffic on those channels along with the simulink timestamp. It could then output a trajectory-like object (though we'd have to be careful about how it 'interpolates') which could be an extract output from simulate or could even be attached directly to the original trajectory objects that are already output from the simulation.