[b] not run precompile asset when deploying to heroku 

- Reason: Heroku precompile assets before setting the database configuration
add username to User model
set up Angularjs
update UI when client click Watch button
[r] use AngularJS to buy instead ajax
[b] client already buy the product
temporarily remove mobile inclusion due to heroku deployment
ignore generated files by assets
not logged in user can view the index and show Product page
when unsigned-in user click on Watch and Buy, the user require to sign in
remove blank lines