Mark email as untranslatable in platform overview

https://bugzilla.gnome.org/show_bug.cgi?id=726538
Set email untranslatable in programming guidelines

https://bugzilla.gnome.org/show_bug.cgi?id=726538
Mark email as untranslatable in platform demos

https://bugzilla.gnome.org/show_bug.cgi?id=726538