Issue #310 - On contact form submit, disable button and change text

On success/failure, enable button, reset text
Merge branch 'devel' into feature/contact_submit_disable
Issue #310 - Contact form behavior

- Disable button
- Change text
- Reset button and form fields
- Button text in html, not javascript
Merge branch 'devel' into feature/contact_submit_disable
Clean up javascript for contact for submission

Spacing, semicolons, order of operations improved.
Use example.com for defaults

Since they are the offical reserved example domains.
btn must be first defined; disable button when submission in progress
Merge pull request #383 from 18F/feature/contact_submit_disable

Feature/contact submit disable