Clean up and finalize Contact interface

Added "Sent" and "Error" messages to the contact page.

 - If send is successful, a message "Your message was sent! We'll try to get back to you shortly" appears.
 - If the php `mail()` script receives an error, the message "Oh no! An error occurred. Please try later, or if the problem persists, let us know by emailing us directly." At this point the direct email block blinks to attract the user's attention.