Specify the index.html file for use with file://

- When using http, the web server searches for index.html when the link
  ends with '/', but when accessing local files, a link to "somedir/"
  does not automatically load "somedir/index.html".
Made the configuration more flexible

- Allow individual asset files to be copied (in addition to a default
  folder).
- Let the user specify the favicon.ico in the html via:
    <link rel="icon" href="/public/favicon.ico" type="image/x-icon">
    <link rel="shortcut icon" href="/public/favicon.ico" type="image/x-icon">
  or something equivalent.
- Let the user specify the base URL and serve URL separately.