Improvements to NTNet and file mechanics

- Small adjustments to NTNet behaviour.
- Adds "undeletable" and "unmovable" flags for computer files. Intended to use for ROM-style programs that are necessary for PC to work.
- Programs now know NTNet status and can act differently depending on this.

code/modules/modular_computers/file_system/computer_file.dm

@@ -4,7 +4,8 @@
 	var/size = 1									// File size in GQ (default 1, do not change unless you really have to). Non-1 values are currently unused but they should be supported.
 	var/datum/computer_hardware/hard_drive/holder	// Holder that contains this file.
 	var/icon_path = null							// !!32x32!! icon of this program
-
+	var/unsendable = 0								// Whether the file may be sent to someone via NTNet transfer or other means.
+	var/undeletable = 0								// Whether the file may be deleted. Setting to 1 prevents deletion/renaming/etc.
 
 /datum/computer_file/Destroy()
 	if(!holder)
@@ -15,4 +16,4 @@
 	if(holder.holder && holder.holder.active_program == src)
 		holder.holder.kill_program(1)
 	holder = null
-	..()
+	..()