Various Lua/C++ stuff, but mainly: Wrappers to call arbitrary Lua methods on tables and objects

Praised the gods who invented variadic templates, it allows for a generic and intuitive (as in "Simon finds it intuitive", YMMV) way to call methods on LuaObjects and LuaTables.

While I wasn't able to identify use cases in the current code, I have several cooking for #1719, and since the general trend is to export lots of stuff to Lua these days, this might come in handy for others.

Cheers,
Simon