add slug to white list
product has many images
use formtastic to render form
basic action for Product controller
ignore uploaded files due to paperclip
add Watch and Buy buttons into Product page
use twitter bootstrap
[b] can not load favicon due to wrong location
restyle show page for Product

- display images
- divide layout
show number of followers
show initial price to let client know
remove unneccessary directories
add User model
add devise to User model
views of devise
header for user: sign in, sign out and sign up
client can follow a product
authenticate user who not logged in
client can follow a product on view
client just follow a product once