Some pre/post related stuff

Reload the onesix version config after the commands (addresses https://www.pivotaltracker.com/story/show/60360652)
Add a few more variables and also substitute them in the command (fixes https://www.pivotaltracker.com/story/show/66994828)

logic/OneSixInstance.cpp

@@ -413,6 +413,11 @@ bool OneSixInstance::providesVersionFile() const
 	return false;
 }
 
+bool OneSixInstance::reload()
+{
+	return BaseInstance::reload() && reloadVersion();
+}
+
 QString OneSixInstance::loaderModsDir() const
 {
 	return PathCombine(minecraftRoot(), "mods");