Added google analytics and basic PV tracking #18

# Changeset
- created google analytics account
- added trakcing code to a template
- creating `analytics.js` dynamically from grunt based on the environment

# To test
1. `grunt`
2. `assets/js/analytics.js` should be empty
3. `grunt --production`
2. `assets/js/analytics.js` should have the contents of `templates/google_analytics.js`