Users should be able to save their item states in their user collection

[skamansam]

Currently, users can't save their state data, so we need a way to do that. There is already state data in the firebase emulator data, so that should be a starting point for this implementation.

• When a user changes an item's state, it should be saved in their collection
• When a list is loaded, it should load the user states and display those

The organization is as follows:

• the userListItemStates collection should have a document for each user, where the document name is the same as the firebase user ID (so the path should be /userListItemStates/{fbauth.currentUser.id})
• the user document should have a subcollection where each subcollection represents a list and has the same ID as the list. (the path should be /userListItemStates/{fbauth.currentUser.id}/{list.id})