Add versions page

[dhobi]

• Add versions.php to web app which shows available library versions for each heroku stack
• Link to this versions.php from the "main" page
• Eat your own dog food by using Relay (with free Upstash for Redis addon) to cache remotely fetched packages.json (save costs, lower response times 😄 )

Demo (Click on: See all versions)
https://php-extensions-v3-a77bf5bcde1d.herokuapp.com/

Last PR, promised!

[tillkruss]

Mhhh, looks like secrets are not available for PRs?

[dhobi]

To be honest, that's the workflow I haven't tested myself. 😞
Not that this automatically means it would have worked otherwise.

[tillkruss]

@dhobi That's fine, secrets might only be available to organization members.