Setup views for subsribe page

Add link to Subscribe page in get-involved sidebar
Fix button.btn-primary issue
New styles for list elements and headings
Complete subscribe.js
Add subscribe() function to function.php and add ajax action
Finish subscribe page view
Add subscribe button on footer
Add Subscription feature

* feature/subscription:
  Add subscribe button on footer
  Finish subscribe page view
  Add subscribe() function to function.php and add ajax action
  Complete subscribe.js
  New styles for list elements and headings
  Setup views for subsribe page
Show error message when subscribe email field is empty
Modify footer nav links
Add mailchimp wrapper class
More left indent for entry ul, ol