Minor QOL changes (CwCheat/Background screen)

[Linblow]

Here's a small QOL PR that will benefit players who spend quite some time in the cheats listing, and or have troubles finding which cheats are enabled.

This adds 3 new simple settings:

1. CwCheatHighlightCheckedCheats under [General] (defaults to true):
   Controls whether the currently enabled cheats should be slightly highlighted (increased opacity i.e. darker background).
   It can be difficult to see which cheats are enabled or disabled in the cheats list, even more so with the background image.
2. ShowPic1OnBackgroundScreen under [General] (defaults to true):
   Controls whether to display the game's PIC1 picture in the BackgroundScreen and therefore, in the cheats listing.
   Setting this to false greatly improves the readability.
3. EnableGameScreenBackgroundAudio under [Sound] (defaults to true):
   Controls whether to play the game's SND0 audio in the background in the GameScreen.

Those settings can only be toggled in the ppsspp.ini file for now.

The UI CheckBox class was added a flag and a method to enable/disable the dark highlight effect in non-image mode.
Note it's disabled by default, and so far, only the CwCheatScreen has a use for it.

[hrydgard]

All of these make some sense, but I also think I prefer different solutions to most of them:

• Instead of a background color change for the checkboxes, maybe we should have a max width, so the checkbox is never crazy far way from the title. Or, on "wide" platforms, put the boxes on the left like in traditional Windows apps?

• Instead of a toggle for the background display, maybe a slider to control how much the background image is darkened, and for the default to be a bit darker than today? That would improve readability similarly.

• A small toggle-able speaker icon on the game screen next to the context menu button, to turn off the background audio?

(Not asking you to implement these, I will, once we agree on solutions)

[Linblow]

I like the idea of the checkboxes being the left, it may help. How about also adding a specific color for the checked icon? Then we could instantly see which cheats are enabled. As for the max width, I believe the issue would remain as it's more of a contrast issue than spacing.

A slider for the background image sounds good, as long as we still have the ability to completely hide the picture (imho). As for the image being darker, I guess it depends on games whether or not it looks better.

Would a toggle-able speaker icon mean it's per-game? e.g if a user explicitly mutes X game, will the choice be remembered for that game and not affect others?

[hrydgard]

I'll think a bit more about the checkbox look.

As for the background toggle and slider, I think I actually might want both...

The mute would only be per-game if you have created a "game config" for that game. Which does seem a little confusing, that's just how settings work in PPSSPP...

[Linblow]

Another thing that may be worth adding is a cheats search filter similar to settings