Postgresdb

Hi, 

I have pushed in code for PostgresSQL Database support. I have also added three gems in Gemfile. They are: 
1. gem 'execjs'
2. gem 'therubyracer'
3. gem 'pg'

Gem #1 & #2 are for the issue "Could not find a JavaScript runtime". I was facing the issue when doing rake db:create. 

Gem #3 is PostgreSQL db support.