Add clearance for auth

https://trello.com/c/WDFJQGlS/32-customer-can-create-an-account
Style sign in/up pages

* Do not show audit form on user auth pages
* Show success message when sign up successful
Fix results error display

Errors when auditing a url resulted in a blank page being rendered to the user.
Use `li` not `h3`

Passing results were being rendered in an `h3` nested within an `li`. This extra
nesting was unnecessary and not expected by screen readers.

https://trello.com/b/PpFdXtix/accesslint-com
Add dotenv
Add segment IO
Add new style for site header
Add basic styles for main content
Add new art assets
Adjust global styles for visual updates
Create result objects instead of hashes

- include auditor and rule js in the app until the js module works
- we should extract these changes back into the gem