[Server support] - Update `CollectionsPage` use-case to use Firebase Firestore/Authentication

[matuella]

Update CollectionsPage flow to use the new structure defined in both #143 and #146.

Ideally, these shouldn't require any changes, but there will be changes to the synchronicity of the events (like networking issues), so it's highly possible that the UI will also change.

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Sub-issue that relates to the Server support - #136.