Refactored LuaTable implementation (New source branch)

[Mytrin]

Greetings,

I've decided to fix https://github.com/arcticfox1919/LuaDardo/issues/10. First commit of this MR contains a simple test, which proves that "next keys" map is not reinitialized after insertion of new key.

I ended up extracting parts of LuaTable to their own classes, so lazy initialization and null checks are encapsulated and easier to maintain.