Rendering of frontend HTML code via templating engine

This is the first part of the HTML5 conversion allowing us to easily change frontend code via a templating engine.

The current functionality should be identical to upstream and will **not** change the UX for now. In the second step we will work on a Bootstrap-based template.

Documentation (doxygen) and examples (README.md) are available in the `templatedoc/` directory.


The previously used code to generate outputs is currently still included (but commented) to allow for easier comparison. This can and will be removed once the merge is accepted and completed.