Implement creating ads

* Actions :new, :create, :show for :ads resource
* Including project_photo uploader
Implement adding tags to user profiles

* Added back in :tag selects in views and tests
* `rails g model Tag name:string`
* `rails g model ArtistTag` with associations to User and Tag tables
* Add `pry-rails` to Gemfile for debugging
* Validations added to ArtistTag for presence of :artist_id and :tag_id
* Need to resolve duplicate records issue for ArtistTag
Fix cumulative tags issue
Implement tagging ads on :create
Implement editing ads
Default image now renders
Refactor AdsController so AdTags save properly
Refactor UsersController to have protected params