Load CSM environment after the restrictions are known

Safety-guards for CSM callbacks to abort on a bad implementation
Only run callbacks when the mods are loaded (and with it: builtin)

Duplication checks inside constructors

src/client/client.h

@@ -397,7 +397,6 @@ public:
 	}
 
 	ClientScripting *getScript() { return m_script; }
-	const bool moddingEnabled() const { return m_modding_enabled; }
 	const bool modsLoaded() const { return m_mods_loaded; }
 
 	void pushToEventQueue(ClientEvent *event);