Update database structure to allow for multiple users

[michealengland]

Currently the database structure is very flat as seen below.

ex:

/posts/postKey/post-data
/timelines/timelineKey/timeline-data

Unfortunately, this makes querying per user difficult as every piece of information will need to be checked. Instead, the data structure should look more like the following.

/posts/uid/postKey/post-data
/timelines/uid/timelineKey/timeline-data

Switching to this type of data organization will allow for much quicker read times since we're reading a smaller portion of data.

[michealengland]

This issue was completed in #74, Timelines & Posts now utilize uid keys to check for data which results in faster lookups and better data organization.