Optimize firebase performance.

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This involves having to keep track of every single listener added to a firebase database reference and removing it appropriately when an activity or fragment no longer needs it.

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This will likely require more knowledge regarding firebase and good practices.

For example, when should objects be stored locally versus just fetching them as you need them? How long should they stay and should they be updated? Maybe keep an offline version of the database (or at least parts of interest?) and update as need be?