Migrations to convert private column to visibility in snippets
Change private -> visibility in Snippet model
Added route for public snippets
Updated public layout to show snippets too
Use new visibility state for snippets
Allow editing of visibility of snippet
Added public snippet controller and views
Added default 'private' visibility to snippets
Adding some tests
Cleaning up some tests
Use new  scope for public snippets
Use snippet visibility partial
Cleaning up some tests