Add Posts

* generate posts migration and model (region_id, category_id, user_id)
* posts resource nested under regions in config/routes
* create posts_controller
* create views for posts#show, posts#edit, posts#new
* _form partial extracted for posts#edit and posts#new
* _errors partial extracted for application
Add Nav Bar, Guest Sign In/Up

*Nav Bar is site wide
*Guest Sign in and sign up functionality works
*Create vanity urls for sign-in, sign-up, sign-out
Admin receives Welcome message and Sign out link
fix errors on these pages EXCEPT routes.rb
remove render commands for partials and deleted 2 routes
remove render commands for partials and deleted 2 routes
fix formatting errors