fix bug 829765 - Redirect apps landing to apps wiki page

This removes the apps landing page, allowing redirection to the Wiki document, as specified in ticket 829765 (https://bugzilla.mozilla.org/show_bug.cgi?id=829765).  

This also moves the signup form to its own page:  https://bugzilla.mozilla.org/show_bug.cgi?id=829756

The newsletter URL will be "/newsletter" for SEO purposes