ACS: Add str GetClassTag(str className). Gets the default tag of an actor class by classname.

Adds a new ACS command: str GetClassTag(str className);

This returns the tag property of an actor class, without the need to spawn said actor first.

Example: log(s:GetClassTag("SuperShotgun")); // Prints "Super Shotgun", which is the SuperShotgun class's tag.

If said actor doesn't have a tag, it just returns the classname.