site.js: Make the current step a global variable
site.js: Strip DOS line endings
site.js: Add a global key press handler

This binds the escape key to show the overview. If already on the
overview, pressing escape returns to start.
styles.css: Set the pointer cursor on send button
site.js: Fix indentation and comments

No functional changes here, but correct the indentation level to step
size of 2 spaces, and provide more verbose comments.
index: Email addresses for message are not optional
site.js: Add message form validation

Validate the contents of the message form and provide visual feedback
for bad data.