Viz: Add command that creates an overview table (index.html) from multiple existing visualization folders

[thequilo]

Reads the visualization data from the script block in the html file. Assumes that the data is dumped within a single line, which does not work for --js-debug.

I also made the file path configurable and changed the default so that visualizations for different systems and metrics are placed in sub-folders. This makes it easier to select different systems or metrics for a comparison index.html file across folders.