Implement fetching and in-memory caching of site icons using SiteInfoProvider

 * Implement /siteinfo/:domain route which fetches standard icon paths
   and scrapes page links from the homepage of the target domain and
   caches the results in-memory.

 * Implement /icondata/?src=<URL> route which returns the data for
   a fetched icon in JPG, PNG or BMP format
Add .gitignore file
Update passcards upstream

  Incorporate fixes for binary buffer decoding in streamutil.readAll()
  and dateutil functions.
Set Content-Disposition and Content-Type headers correctly for /icondata route

This enables the /icondata URL to be viewed directly in the browser
and used as the source for image tags etc.