Modernize HTML templates

[wvteijlingen]

I noticed that the HTML output is somewhat dated, and I think it can be improved in several ways:

1. Drop support for IE. This means we can remove all shims.
2. Drop jquery. Everything can be done using vanilla JS nowadays.
3. Drop bootstrap and use minimal custom CSS to achieve the same result.
4. Merge all output in one HTML file.

I think specifically the last improvement would be nice. It will make it much easier to deploy an xcov artefact on CI systems. Instead of having to copy or zip up a whole folder, everything will be nice and contained in one HTML file.

I can take a shot a creating new templates, if people are open to it.