Previously, flame-graph view could only display filefunctions
granularity. We can now support all the available granularities.

This allows the user to supply a granularity either via a command-line
flag (e.g., --files), or as a URL parameter (e.g., ?g=files).

Details
* Made the default initial granularity "" so that we can stick with
  the default flame-graph granularity of "filefunctions" while also
  allowing overrides.
* Use different computation of the list of shorter display names
  for file names (strip off leading path components instead of package
  prefixes).
* Similarly compute color based on directory name instead of package name.
* Include line number and column number in displayed names if the
  granularity includes line numbers.