Inject Enceladus version into index.html upon build instead of gettinq it via request upon display

## Background
Right now the Enceladus version - used for caching (in)validation - is gathered upon the page load via an extra request. Making the version info static would bring several benefits.

## Feature
Make ti, that the version is injected directly into the `index.html` file directly upon build. That will remove the necessity of the asynchronous call upon displaying the page.
That simplifies the logic, adds robustness and speeds the page load.