Split expansion mission categories in Allied and Soviet

It's not always apparent from the title which faction a mission
belongs to, and players may want to know beforehand
instead of having to guess.

mods/ra/missions.yaml

@@ -29,18 +29,20 @@ Soviet Campaign:
 	soviet-09
 	soviet-11a
 	soviet-11b
-Counterstrike:
+Counterstrike Allied Missions:
 	sarin-gas-1-crackdown
 	sarin-gas-2-down-under
 	sarin-gas-3-controlled-burn
 	fall-of-greece-1-personal-war
 	siberian-conflict-1-fresh-tracks
 	siberian-conflict-3-wasteland
+Counterstrike Soviet Missions:
 	soviet-soldier-volkov-n-chitzkoi
 	top-o-the-world
-Aftermath:
+Aftermath Allied Missions:
 	production-disruption
 	monster-tank-madness
+Aftermath Soviet Missions:
 	shock-therapy
 	situation-critical
 OpenRA Originals: