Updated saving

Since @Protuhj is on holiday, I've taken #1323 and fixed some issues with the menu myself. I have not touched any of the saving code.

* Combined START & LOAD on main menu to take you to the slot selection screen
* Redid the load menu so it looks more like the pause menu
* Selecting an occupied slot will warp you to your savepoint
* Selecting an empty slot will begin a new game, starting with the scanning animation

"Quit to menu" doesn't work, but does if you merge master. Do I need to do that?

Do we want the words "new game" anywhere?