Website should list available architectures for each image

[ES-Alexander]

We do this on the real store, and it would be helpful for users (and developers) to be able to know in advance if a build is available for their architecture.

In BlueOS the determination is with a set of the architectures of all the images, which are then listed on the Extension card.

[ES-Alexander]

Could help to identify things like #95 without needing a local build of BlueOS, or having to read/parse the manifest file.