Fix bug 874525: Redirect NSS/* and JSS/* to MDN.

Commit 98b4668f redirected the NSS and JSS directories to MDN. This
commit additionally redirects the files and directories that live below
them to MDN.
Redirect /mobile/customize for Bug 876668
Merge pull request #947 from openjck/bug-874525-redirects-1
Bug 877165 - Remove/redirect /firefox/connect page
Merge pull request #949 from sgarrity/bug-876668-redirect-mobile-customize
Merge pull request #948 from sgarrity/bug-877165-remove-connect
Fix bug 653876: Add l10n helper for images.
Merge pull request #907 from pmclanahan/add-image-l10n-helper-bug-653876
[Fix Bug 879867] Return 403 on csrf failures
Merge pull request #951 from Sancus/master