JSON export doesn't differentiate public from internal comments

Summary

Currently, when exporting a SD request to JSON format, it's not possible to tell which comment is internal or public from the JSON file.

Steps to reproduce

1. Go to Manage add-ons -> All add-ons -> jira-importers-plugin -> Enable JSON export
2. Create an SD request and add one internal and one public comment
3. Export the request to JSON from its View Screen -> Export

Expected behavior

The comments can be differentiated with a visibility or internal/public parameter

Actual behavior

The comments only contain comment body, author, and date info:

"comments" : [ {
        "body" : "Hi JIRA Admin,\n\nPublic\n\n– JIRA Admin",
        "author" : "admin",
        "created" : 1469704703000
      }, {
        "body" : "Hi JIRA Admin,\n\nPrivate\n\n– JIRA Admin",
        "author" : "admin",
        "created" : 1469704718000
      } ],

Note

A REST API endpoint can be used to retrieve and differentiate between internal and public comments:

/rest/api/latest/issue/<issue_key>/comment?expand=properties

e.g. http://localhost:8080/rest/api/latest/issue/DESK-1/comment?expand=properties

Reference: JSD-1261