Remove old dataviz stuff. Optional directory serving static files.

• Turned old index.html file into a /stats.json API call. (follow the /head.json "convention")
• Added optional feature to serve static files from any directory. It will be used in order to serve the new data visualization tool. Having symlink resolved is useful for teztale-dataviz routing to work, otherwise file without extension (such as the one used to simulate the "Level" page) will be downloaded by the browser instead of being used as a HTML page.

I tried to be the most generic possible (act as a server delivering static any file) while being possible to use teztale-dataviz with it.

In order to use teztale-dataviz, we will use its current release and add symlinks for all pages to point to index.html so sharing urls will work. It's a hack, but it's the only way to use a single page app with react-router (and probably any single page app) and it's okay to do so imho.

About|DelayToConsensus|DelegateStats|CommitteeSizePerDelay|CommitteeSizePerLevel|Level -> index.html