Consolidate press kit redirects for Bug 957664

This replaces a set of redirects for various URLs under/around /en-US/press/kit/.

It also adds en-US/press/kit.html to the redirects, as it was missing previously.

The following URLs should be redirected:

http://www.mozilla.org/en-US/press/kit-3-6.html
http://www.mozilla.org/en-US/press/kit-4b.html
http://www.mozilla.org/en-US/press/kit-N900.html
http://www.mozilla.org/en-US/press/kit-android.html
http://www.mozilla.org/en-US/press/kits/

I'll be submitting a patch to remove the old redirects from the SVN/PHP site .htaccess on [Bug 957664](https://bugzilla.mozilla.org/show_bug.cgi?id=957664)