Alt art grouping

[NBKelly]

The regex will probably need to be adjusted for alt versions of flip cards, but that's a bridge that can be crossed later.

The output on mongo looks like this, for a case with two versions of overclock in the same folder:

Closes #8004

[NBKelly]

ok this was a nightmare to actually figure out, but I ended up with something that:

1. works
2. maintains compatability

Essentially, we're already storing arts on cards as 1-ary lists (I don't know why), so we can just store multiple things in those lists instead.

On the cardbrowser, we now seperate it by item in each list, rather than just by each list.

When you select an alt art, it now indexes code [key idx], instead of code key.

When looking at a card art, we then check if art is sequential: if yes, we fetch the list of arts, then pick the art at the given idx.
If no, then we just do what we already do which is yield the first item from the list.