Update Gisconverter to new version, move to composer.json, fixes T539

Summary:
- switch to Symm/Gisconverter, update license
- rebase toGeoArray patch [with PR](https://github.com/symm/gisconverter/pull/8)
- switch from submodule to composer
- change usage to match new structure

Test Plan:
```
git submodule sync
composer update
bin/behat -f progress -c application/tests/behat.yml application/tests/features/posts/api.geojson.feature
bin/phpunit -c application/tests/phpunit.xml application/tests/classes/Util/BoundingBoxTest.php
```

Reviewers: rjmackay

Reviewed By: rjmackay

Subscribers: srutto, bodacea, dkobia

Maniphest Tasks: T539

Differential Revision: https://phabricator.ushahidi.com/D261