[Toaster] Design - Custom images page (8091)

[Barros Pena, Belen]

I've documented the page where you see all the custom images created
within a certain project, and opened the corresponding Bugzilla entry:

https://bugzilla.yoctoproject.org/show_bug.cgi?id=8091

Design document attached to it, as usual.

Any questions / comments, let me know.

Thanks!

Belén