Replace backbone model with backbone model factory

Summary:
Fix for #346.

Replace `Backbone.Model({});` with `Backbone.ModelFactory({});`

Test Plan:
 - Make sure API explorer is enabled
 - load #apiexplorer
 - Initiate any of the API endpoints
 - See the endpoint get executed

Reviewers: shadowhand, rjmackay

Reviewed By: rjmackay

Maniphest Tasks: T346

Differential Revision: https://phabricator.ushahidi.com/D172