Supporting new file name specification

Supports both old style:
  arguments.filename.default "..."
  arguments.filename.values []
and new style:
  arguments.files.image "..."
  arguments.files.composite "..."
Compatibility changes for visualization model for "value images".

The info file will have two types of fields:

  1. RGB fields that can be copied directly to the composited image
  2. Value fields that must be processed

attributes.fields will contain only RGB fields, while
attributes.scalars will contain the value fields
Fixing file name search order in docstring.
Merge pull request #23 from Kitware/info-file-format-changes

Info.json format changes