Modular Computer Multitasking + Fixes

- Modular computers now support multitasking.
- New hardware type added. Basic CPUs may be obtained when purchasing a laptop or tablet, Photonic CPUs can be printed at research at imprinter. This hardware piece determines how many programs can be on background.
- Programs can now have an icon that is rendered in main UI's header (along with the power icons, etc.) when the program is on background. As an example, these icons have been added to NTNRC client (Dark icon when no messages have been received, blinking when new message is waiting), Alarm monitor (Blinking red when an alarm is active, green otherwise) and downloader program (Animated arrow when downloading, stationary when finished.)
- Adds missing crew monitor icon to tablets. Fixes #11937

code/modules/modular_computers/file_system/program.dm

@@ -18,6 +18,8 @@
 	var/available_on_ntnet = 1				// Whether the program can be downloaded from NTNet. Set to 0 to disable.
 	var/available_on_syndinet = 0			// Whether the program can be downloaded from SyndiNet (accessible via emagging the computer). Set to 1 to enable.
 	var/computer_emagged = 0				// Set to 1 if computer that's running us was emagged. Computer updates this every Process() tick
+	var/ui_header = null					// Example: "something.gif" - a header image that will be rendered in computer's UI when this program is running at background. Images are taken from /nano/images/status_icons. Be careful not to use too large images!
+
 
 /datum/computer_file/program/New(var/obj/item/modular_computer/comp = null)
 	..()
@@ -35,6 +37,11 @@
 	temp.usage_flags = usage_flags
 	return temp
 
+// Relays icon update to the computer.
+/datum/computer_file/program/proc/update_computer_icon()
+	if(computer)
+		computer.update_icon()
+
 // Attempts to create a log in global ntnet datum. Returns 1 on success, 0 on fail.
 /datum/computer_file/program/proc/generate_network_log(var/text)
 	if(computer)