Add bounded arena

[joefresna]

At the moment the multiagent particle simulation have periodic boundary conditions (torus).
Add walls and either:

• let the particle bounce on the walls (as molecules do)
• let the particle get stuck to the wall (as simple robots do)

[jarmarshall]

Shall we stick with periodic boundary conditions for the first release?

[joefresna]

Yes, I would put this in the Second Release ;-)

[jarmarshall]

I'm making a Second Release milestone now - it would be useful for some other issues I'm sure...