Allow to specify remote receivers in addition to local SimulationInfo destinations.

Renames SimulationInfo class to SimulationReceiver, and allows to
instantiate it with a liblo-style URL instead of a Simulation's
lo_address/queue.

Adds possibility of specifying multiple `-s' options on the command
line and following the simulation spec string with a liblo URL.

This means that if Dimple is executed on one computer with "-s v", and
on the other computer with "-s ph -s v,osc.udp://<hostname>:7773",
then the haptics and physics simulations will run on one computer, and
send visual update messages to the remote computer that displays the
graphics.
Add a command-line option to specify the listening ports.
Fix whitespace in help output.
Allow adding simulations after startup, on message /world/add_receiver.

A simulation can now be started e.g. with "-s hp", and another
instance of Dimple can be executed with
"-s v,osc.udp://<hostname>:7774", where 7774 is the Interface port,
and the first instance will use the second one for the visual
simulation.  Similar with physics or haptics.