Add Phinx migration tool, replaces Minion, fixes T235

Summary:
- add phinx to composer
- add phinx config, passes kohana config into phinx
- add initial migrations: database structure and relations

Test Plan:
**Back up your existing database!** and create a new one, then run phinx:

```
bin/update
bin/phinx migrate -c application/phinx.php
bin/behat -f progress -c application/tests/behat.yml
```

Reviewers: dkobia, eyedol, rjmackay

Reviewed By: rjmackay

Subscribers: srutto, bodacea

Maniphest Tasks: T235

Differential Revision: https://phabricator.ushahidi.com/D239