Profiles made completely public.

Fixes #5

  * Refactor ApplicationHelper.navigation_items to work for both signed in and signed out users
  * Remove HomeHelper since navigation is handled by ApplicationHelper
  * Add guest abilities for signed out users
  * Use exposed profile and current_tag to build page title
  * Add tests for signed in and signed out navigation items
  * Update specs to have signed out requests be successful instead of redirecting
  * Remove authenticate user before filter from controllers
  * Only fire refresh gist before filter when a user is signed in
  * Refactor MyGists::Cache spec by mocking Rails.cache
  * View cleanup by highlighting and bolding 'gists' and tag names
  * When a user searches for a profile which does not exist, make sure no gists are found
  * Add tag tooltip to search view