reimplemented user registration script

Rewrote the script (in PHP) that collects user registration data and
generates emails to the user and the protege-registration mailing list.
Replaces an ancient Perl script, used in the current website.  Will be
used with the newly redesigned Protege website.
new code for user registration modal dialog

Modified existing and added new code for the "sign up for Protege" modal
dialog to do data validation, resetting dialog contents after dismissal,
and do form submission via ajax.
fixed formatting
removed console.log statements
added target
content updates for support section
updated link to webprotege local install