Refactored code to support multiple database engines

Application can now support multiple database engines.
Added config file for dev/prod mode

Added a configuration file to easily distinguish between development
and production modes.
Added PostgreSQL database wrapper (#9)

Added a Database class that wraps around PostgreSQL basic functionality.
Updated schema (#9)

Updated database schema to adapt to PostgreSQL.
Removed support for multiple database engines (#9)

Removed support for multiple database engines as abstraction became
difficult to implement.
Changes in queries to reflect new schema (#9)

Changed how parameters are passed to queries (using %s) and how times
are saved.
Added psycopg2 module to requirements.txt (#9)
Updated .gitignore

Removed .DS_Store files from repository.
Housekeeping

Changed environment to production and removed the host from app.run().
Merge pull request #10 from linkyndy/postgresql-integration

Postgresql integration