Update autocompleter to accept JSON generated using the JSON plugin

The autocompleter expects a JSON array of 2 dimension arrays. The JSON string generated using the JSON plugin will always be an object. Modify the autocompleter to do the following:

If response is of type object, try to find a field with the same name as the autocompleter, if found, use its value as the datasource, if not, use the first array found.
If the response is not of type object, assume it is an array and use it as datasource (current behavior)

Compatibility won't be affected by this improvement.