Fixes html indentation and missing closing tag

The convention in this repository seems to be 4 spaces for indentation, so you may aswell actually write this down for editors in an .editorconfig file which many editors will follow. While i do not like spaces as indentation, it is better to have uniform indentation with spaces, than not have uniform indentation.

Now this MR does not only swap out all tabs for 4 spaces but also indents the html according to its hierarchy.