Gamelist: Add 4x resolution nobanner image

[Dentomologist]

When a game hasn't generated a GameList banner yet Dolphin displays an X placeholder image. This PR adds a 4x resolution version of the placeholder. It also improves centering of 2x and android banners, and adjusts 1x banner to increase consistency with other resolutions while maintaining sharpness.

[JosJuice]

Please also update Source/Android/app/src/main/res/drawable/no_banner.png.

[Dentomologist]

Android nobanner now changed as well.

[MayImilae]

"Add antialiasing to 2x" it wasn't aliased, it was just sharp. :/ And I can provide a sharp 4x as well if you were worried about them matching.

[Dentomologist]

So it turns out the 2x image already had antialiasing, but the color change used was subtle enough that I missed it. The 1x image had a larger color gap which I copied for the other resolutions, which ended up looking blurrier than what the 2x had before.

I've redone the other resolutions to match the 2x banner colors.

Note: The file size reduction isn't present in this version; I want to address any other issues first before redoing that.

[MayImilae]

Here you go, a full fixed set of nobanner icons. I created a true symmetrical version that fixes the weird positioning at any size, simply by being symmetrical. However this symmetry means that when the X meets, the joints are two pixels across. This is fine for the larger sizes, but this makes the original 1x version look worse (hence where the weirdness came from, I optimized for 1x). So for the best of both worlds, I made a new 1x icon that is non-symmetrical but gives the perfect single pixel intersection. And since these are straight from my source vector PSD so everything is perfectly crisp.

Optimized with optifine.

nobannerfixed.zip

[Dentomologist]

Thank you for the images, I've updated the build with them.

The 4x and android versions had their rightmost column slightly transparent, so I made them opaque and reran them through optipng.