Redesign object store preferences

[itisAliRH]

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[bgruening]

Jumping in here, because the file-source UI looks similar, and should probably be updated as well.

I'm still not sure how EU will handle many of the cool file-sources we have: https://github.com/usegalaxy-eu/file-source-plugins/ should we just enable them by default for all users or add them as templates, so users can opt-in. If we offer them as templates, it would be nice to maybe make this site searchable.

Long story short, maybe we should consider adding a search-interface to the file-sources UI.