Parameter q be modifiable for queries

An option to change the query parameter q to another value would allow the custom callback functionality of this module be more robust.

Proposed solution

1. Create a new variable call query_parameter (or whatever) to store the value of custom query parameter name.
2. Add a new text field under the radio select option for custom callback on the edit search autocomplete form to allow user to enter name. If blank, then q will be used.
3. Pass custom query parameter to the javascript of Search Autocomplete via settings array. (Pass q if textfield from step 2 (above) is blank.
4. Create an ajax request using javascript query_parameter instead of only q. (had a problem with cross-domain and google. https://www.drupal.org/node/2720931 → )

This along with https://www.drupal.org/node/2721721 → would make this module very robust.