basic authenticate
create_user now checks if username exists
added change_password
added test cases
Merge pull request #13 from projectcs13/sprint2.db_api_authenticate

Sprint2.db api authenticate
* Fixed so that it is easy to generate and clean the documentation.
* Fixed so that website/ is actually buiding using rebar by adding an otp .app.src file using the ./rebar script
Merge branch 'develop' of ssh://github.com/projectcs13/sensor-cloud into sprint2.project_structure