* Add a separate FindLuaJit.cmake
* Remove LuaJit from our modified FindLua51.cmake
* Make use of the new FindLuaJit
The reason for splitting them up like this is so we can have a
preference for LuaJIT that's not determined by the search order in
FindLua51.cmake as well as giving the server operators the choice to
prefer normal Lua with the EQEMU_PREFER_LUA cmake option
