NTNet P2P Transfer client

- Adds simple NTNet P2P transfer client, that allows users to send files via NTNet.
- This client can act either as actual client (downloading files), or as a server, providing one file at time.
- This may (not guaranteed) be expanded in future, to allow sharing of multiple files at once, possibly even having some sort of dedicated server architecture
- Transfer speed is calculated as lower value of connection speed of both devices (weakest link in the chain)
- Server may be protected using rudimentary password that, if set, must be entered to download the file.

code/modules/modular_computers/computers/item/modular_computer.dm

@@ -75,6 +75,7 @@
 	..()
 
 /obj/item/modular_computer/Destroy()
+	kill_program(1)
 	processing_objects.Remove(src)
 	if(network_card)
 		qdel(network_card)