LuaStack

Renamed LuaConverter into LuaStack (might be readded in the future)
Added operator= syntax for pushing values onto the LuaStack
LuaTable

Templated LuaTable to fill a lua table with key-value pairs
Moved Tuple.h into LuaTypes folder
Minor changes of LuaTypeTraits to be index safe (lua_remove cannot
accept negative indexes, custom luaL_remove can)
Moved several functions from LuaTypeTraits.h into impl.h