Json files is handled as an uneditble attachments in the current 

version.

I implemented a new class JSONReviewUI that

enhence Review board's ability to process JSON file.

New features include:

Rendering JSON in an easy-to-read format.
Allowing the user to comment on the prettified file based on 

   line numbers.
Auto-sorting of output keys.
Allow user to compare the changes of files in diffs
A thumbnail that render in the easy-to-read format, too.

Ran unit tests.
Tested the development environment with:

Properly formatted JSON files.
JSON files with long lines.
Minified JSON files.
Highly-nested JSON files.