Refactor profile image code to use the photos/ tree in Firebase

[kjdillon]

This includes both modifying the upload logic to upload the profile image to the photos/ tree, as well as modify the code that accesses the profile images to get them from the photos/ tree. In the users/ tree the key for the profile image should be stored for each users profile image.

[kjdillon]

This is high priority because the database has been restructured and people cant sign up again until this happens. @imranyousuf @cshort12