Pluralize header in groups index.

Fix navbar to allow non-signed-in user to be able to view all groups
feature when user post with tag
Create tagging model and migration
Create Tag model and database
Users can write multiple tags for post
Refactor unused lines
Add new Sprint gem
CSS styling for layout
Comment association with tags
Change wording
update schema
Fix changed words in spec and navbar
Change Tag to Tag list to match form label
Refactor Post model  tagging methods
Merge branch 'master' of github.com:jmoon90/studygroup