Add info_exists boolean to files on container list endpoints

[nagem]

Allows clients to optionally show "view info" when file has an info field that was withheld (on list endpoints).

New endpoints

List endpoints will get a new key on files: info_exists, a boolean.

Example:

GET base_url/api/sessions/<session_id>/acquisitions

[
  {
    "files": [
      {
        "origin": {},
        "info_exists": true,
        "measurements": ["localizer"],
        "name": "149_1_1_localizer.dicom.zip",
        "created": "2017-07-19T17:54:00.355000+00:00",
        "modified": "2017-07-19T17:58:01.127000+00:00",
        "type": "dicom",
        "modality": "MR"
        ...
     

Breaking Changes

None

Review Checklist

• Tests were added to cover all code changes
• Documentation was added / updated
• Code and tests follow standards in CONTRIBUTING.md