Replace Imagefly module with composer, refs T539

Summary:
- updated to latest version of Imagefly
- modified and sent PR for `source_dir` addition: https://github.com/Bodom78/kohana-imagefly/pull/12
- updated module reference and config

Test Plan:
```
git submodule sync
```

Manually verify that output of API call to `/media` works as expected using the API explorer.

Reviewers: eyedol, rjmackay

Reviewed By: rjmackay

Subscribers: srutto, bodacea, dkobia

Maniphest Tasks: T539

Differential Revision: https://phabricator.ushahidi.com/D265