Merge pull request #10 from linkyndy/postgresql-integration

Postgresql integration
Resolved merging conflicts
Added pyechonest to libs
Changed requirements.txt
Added an Echonest wrapper (#7)

Added a class that conveniently wraps the Echonest API.
Changed schema (#7, #9)

Added a songs table and moved several columns for database
normalisation.
Adapted some column types to PostgreSQL (SERIAL, TIMESTAMP).
Integrated the Echonest wrapper (#7)

Integrated the Echonest wrapper in existing code.
Added models, refactored code

Added new models that reflect the new schema and also refactored code.
Added a Soundcloud wrapper

Added a class that conveniently wraps the Soundcloud API.
Merge pull request #18 from linkyndy/echonest-integration

Echonest integration
Refactored code
Removed /libs folder (#17)

Removed all SDKs from the /libs folder and added how to install them in
the documentation.
Reorganized files (#11)

Reorganized files in folders (models, wrappers, database) and fixed
include issues between them.
The spp structure should now be clearer :)
Added Facebook wrapper (#20)

Added a class that conveniently wraps around Facebook API.
Removed .DS_Store
Merge pull request #22 from linkyndy/code-refactoring

Code refactoring
User_artist relations save independent to artists (#19)

User_artist relations now save independent to artists. That is, they
save no matter the artists have already been saved or not to the
database before.
Echonest artist fetch on suggestion request (#15)

Echonest data for artists is now retrieved only when a user request a
suggestion and that particular picked artist does not have Echonest
data attached.
Bug fixes and refactoring
Added method that returns list of artist ids (#19)

Added a method that returns a list of artist ids given a list of artist
Facebook ids. Helper method used for saving user_artist relations.