create category followers table
add category_followers relations on user and category
create following_this_category? method on user
controller to handle with user subscription into category
show category name and link to subscribe on explore
category follower specs
User#following_this_category? specs
specs fo categories/subscriptions_controller
show credits warning when user has less than R$ 10
added scope into projects to get the projects of the week
added scope into user to check if user already receive some notifications from categorized_projects of the week
create category_notifications
scope to check if category has projects on current week
category has_notifications
method to deliver the notification of projects of the week
categorized_project_notification
rake task to deliver categorized notification
added specs for Category.with_projects_on_this_week
specs for category new methods
use AT TIME ZONE on queries