Add global namespace to Acedia actors and objects

We want all actors and objects defined in Acedia to share
a global namespace that provides an access to important variables
(such as `Acedia` reference) and functions.

We add a `Global` singleton and `AcediaActor` / `AcediaObject`
base classes with a quick accessor to it's instance (`_` / `_()`).

sources/Acedia.uc

@@ -49,6 +49,7 @@ event PreBeginPlay()
     }
     default.selfReference = self;
     //  Boot up Acedia
+    Spawn(class'Global');
     LoadManifest(class'Manifest');
     LaunchServices();
     InjectBroadcastHandler();   //  TODO: move this to 'SideEffect' mechanic