adding categories model
new categories controller, Check the the admin validation
tests for categories controller, just the basic ones
resources for categories
new Course model and new validations for it
courses controller with its tests
new field image_url and tests for it
new index
video model was added and some new validations
videos controller with its test and few new validations
Merge pull request #8 from rbarrera87/8-Categories-Courses-and-Videos

Create Categories, Courses and Videos