If a column is payload or contains _payload it will be assumed
it has JSON data in it, then we will show the truncated JSON in the
result column with a button to show the full-screen formatted
JSON using our full-screen code viewer. We also do the same if
the column is the `json` postgres data type.
This commit updates the plugin to the latest guidelines, as shown in
discourse-plugin-skeleton, which involves moving a lot of the code to
dedicated files, use proper namespaces, use the autoloader as much as
possible, etc.