More shortcuts for the Windows version

I added and changed some shortcuts.

F3 changes the current savestate slot that are used with F2 and F4.
Fast speed was moved from F3 to F1.
The emulation is paused and resumed with the 'Pause/Break' key.
F7 enable or disable the option "Skip Updating PSP memory". It helps to see the differences when the option is used.
F8 is now unused.
Ctrl+W stops the emulation and returns to main menu.
Ctrl+B resets the game. A better key could be used instead of B.