Public API endpoint to request server information

[mstevens83]

It would be a good idea to have an API endpoint which non-human clients (e.g. Sapelli) can use to request basic server information (version, installed extensions, etc.) and thus verify they are indeed talking to a (compatible) GeoKey set-up.

There could be security concerns with giving away this information in a public API, but then again we already expose the GeoKey version on publicly accessible admin pages.
To reduce the risk @mfc-julius points about the API should not expose superuser extensions unless the requester is an (authenticated) super user.

[mstevens83]

Implemented in 96171e4, 04671e5 & a58164c.
Merged into master and released with https://github.com/ExCiteS/geokey/releases/tag/0.8.2.

Still, I'm interested to hear what @oliverroick thinks about all this.

[mstevens83]

Added documentation on website: ExCiteS/geokey-website#19