(feat) Created trackPost and trackUser basic feature using Firebase events

Firebase sends an event whenever data is changed/added to a specific endpoint. I use this functionality to create a basic trackPosts and trackUsers feature. 

TODO: right now it (1) uses a hardcoded example for a user and post and (2) just console logs the data, so we need to integrate this into angular and allow the user to enter a specific user or post and then use this instead of the hardcoded data. Should be fairly straightforward.