Remove backbone-model-factory from App dependencies

Summary:
- Remove backbone-model-factory from App dependencies
- Explicitly require backbone-model-factory in each model
- Remove search filter model
- Don't use modelfactory for API Explorer Model

Fixes T341

Test Plan: - Load UI and check models work as expected

Reviewers: dkobia, shadowhand

Reviewed By: shadowhand

Maniphest Tasks: T341

Differential Revision: https://phabricator.ushahidi.com/D167