SinglePlayer -> Singleplayer
SP menu signal/slot hookup, show create/load world
no need for the exitClicked() signal in main menu, just call the

ClientBackend slot specifically and we're good. works well through SP menu
as well
createworld signal working, to propagate upward to stackview
rm window.rml
no more gui.h/cpp
lots of cleaning house, removing librocket leftovers (still a lot to do)