(NDK) Added explicit initialisation

Components and systems just can't be initialized at startup, so we need
some kind of explicit initialisation. I followed the same layout as the
others modules by adding a core class (Ndk::Sdk) which will initialize
components and systems, and Nazara's modules.

This is starting to get serious, I like it.


Former-commit-id: 263500e8d16db70ef7f92047b8a7e3235c08bcd0

SDK/src/NDK/BaseSystem.cpp

@@ -40,5 +40,5 @@ namespace Ndk
 		NazaraUnused(entity);
 	}
 
-	SystemIndex BaseSystem::s_nextIndex = 0;
+	SystemIndex BaseSystem::s_nextIndex;
 }