Push Tag_capability branch to group project's Tag_capability branch

This serves as the major file push to add tagging capabilities to the project.

The ActsAsTaggableOn gem is added to the Gemfile, acts_as_taggable_on is placed into the Chapters model, and four database migrations are created. The majority of functionality resides on the ChaptersHelper, with seven tag Class methods, two tag instance methods, and a tenth method allowing for searching by category. In addition the Chapters table column "tags" is renamed to "tag_list", the ChaptersHelper is included in the Chapters controller, and a through table relationship on the User and Chapter models is established.