Bug 764035 - [SEO] Implement schema.org for applications

* Reused the description of the page; no need for extra l10n
* Declared both `http://schema.org/SoftwareApplication` and `http://schema.org/Product` in case
* [Structured Data Testing Tool](https://www.google.com/webmasters/tools/richsnippets?q=uploaded:8004e740aacfb29e23845b6e44f101b1)