Bug 11002: (follow-up) use jQuery validator plugin

Bug 11002: (follow-up) use jQuery validator plugin

This patch uses the jQuery validator plugin introduced in
bug 6209 for two reasons:

[1] To supply validation for non-HTML5-compatible web
    browsers.
[2] To force use of the validator plugin rather than
    built-in validation for HTML5 browsers, which means
    that our translations will be used.

Note that a version of the function to prevent double form submission
is used as the submit handler invoked when the validator plugin
is satisified that the form is complete.

To test:

[1] Same as the main test plan, but note that the validation
    messages now appear inline rather than as pop-ups.
[2] Verify that the double form submission prevention still
    works.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>