Moved config file

Removed package since a single file is sufficient for configs. Removed
classes since config keys are stored in environment variables.
Moved files from / to /instasong
Moved models from /models/ to /instasong/models/

Also ditched old models and renamed them. Will clean up mess in later commit.
Moved app creation logic
Added app manager script
Added tests folder with base test class

Configured based test class for ease of SQLAlchemy use within tests;
Added also some sample tests (will be cleaned in later commit).
Refactored artist model and written tests
Added unique constraints to model fields
Added drop database command in manager.py
Added facebook test users to facebook_wrapper
More refactoring on artist model and written some more tests
Refactored user model and written tests
Moved user_artist to a table only and a ManyToMany relationship
Updated wrappers

Updated how the app is imported to wrappers;
Also, wrappers return None where appropiate, instead of reraising
exceptions.
Refactored song model
Updated user and artist models

Logic update in User model and refactoring and wrapper update in Artist
model.
Updated config.py (#40)

Added RethinkDB config vars;
Removed PostgreSQL config vars;
Cleaned and grouped rest of config vars.
Updated requirements.txt (#40)

Added RethinkDB related packages;
Removed PostgreSQL related packages;
Updated and grouped rest of packages.
Updated manage.py database commands (#40)

Database-related commands in manage.py are now adapted to RethinkDB;
Changed also how RethinkDB is initialized app-wide.
Pluralized tables in manage.py (#40)

Database tables are now created by pluralizing their corresponding
model names.