Add a global fallback image for downloadboxart

[tetra4]

https://github.com/lifehackerhansol/YANBF/blob/395cb29b9dc272d8d219b66b89e36b295e528e44/generator/core.py#L278-L280

When creating a forwarder for a game not in the GameTDB, the creation of the forwarder will fail.
My particular use case involves valid software (DSiWare), of which I had to add a generic image into multiple games to get them to pass.

Please consider adding a default banner image.

[lifehackerhansol]

That would actually be a really good idea... but what do we make the fallback image? Any suggestion?

I'm really not a designer, so I'm out of ideas here.

[lifehackerhansol]

Also also... if it's DSiWare, consider just installing it. I'm not particularly happy about the use of DSiWare with YANBF because of compatibility concerns with nds-bootstrap and other things. Understandably there is that 40 title limit, but at least it is 40 for real DSiWares now instead of NDS games.

[lifehackerhansol]

I gave this more thought.

At most, what I can do with my limited knowledge is to just stretch the icon by 20x to fit as the banner. But that's going to look t e r r i b l e...

Yeah I'm just drawing more blanks with this one.