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
Merge pull request #21 from Kitware/refactor-app-view-structure

Refactor app view structure
adding model describing displayed layers
rename unserialize
Merge pull request #24 from Kitware/layer-model

Adding a layer model
Fixing file name search order in docstring.
Merge pull request #23 from Kitware/info-file-format-changes

Info.json format changes
Merge remote-tracking branch 'origin/master' into search-page-and-routing
Reorganize search layout, add layer controls toggle