create Product scaffold

Generate a scaffold for the products table with title, decription,
image_url, and price columns.
seed products

Seed the products database with entries for three convenience stores.
create products stylesheet and template
add Product validations
add fixture

Added a fixture and incorporated it into the unit tests.
add length validation and custom error message

Per Ch. 7 exercises, added a validation for a minimum title character
length and made a custom error message for it. Also added a unit test
for it.
store controller, views, functional tests

Create a store controller to control customer interaction, improve the
views, format prices by US convention, and write functional tests.
cleaning up