main.cpp, menu.cpp: Correctly reimplement saved states while allowing for the emulator to back out of loading a saved state to preview it.

Some SAL changes are required to hold the per-platform temporary directory to hold the state required to back out of the load.
Incorporate a new background and selection bar courtesy of hi-ban. The background is a recreation of a SNES game box.

menu.cpp: Load and display the background. Raise the menu text by 36 pixels. Raise the saved state and ROM selection menus to fit. Remove the "selection bar" behind the ROM path and change its color not to be white.