implement route that returns user's last month of fitbit steps data

At the moment, it makes an on-demand call to Fitbit's API and returns back a blob of the last month's steps data.

This commit includes the following working routes:
GET '/users', Gets all users' info.  Will probably not keep this around...
GET '/users/:id', Gets user's info specified by the id, at the moment, id must match current logged in user's id
DELETE '/users/:id', Deletes user info specified by the id, at the moment, id must match current logged in user's id
GET '/users/:id/fitbit/steps', Get last month's fitbit steps data for the user specified by the id, at the moment, id must match current logged in user's id