Add users to search capabilities

*Add ability to seach usernames
*Add users to search results
Add linking for @username

* Add helper and method to find and create link
* Add method to text_shout view
Add hashtag capabilities

* Add ability to find and link to seach for hashtags
* Add method to view
Make html edits

* Add headers to sign in/sign up
* Pluralize follower/following counts
* Add home navigation
* Make minor spacing/tagging changes