Prototype of DCI, using the Config entity, refs T172

Summary:
- demonstration of using entity, repository, storage interfaces
- PSR-2 compatible code
- custom PSR-0 autoloader
- addition of Pimple for DI container
- global `service()` function

Test Plan:
Integrated with `config` endpoint, can use site settings to verify that GET/PUT works as expected.

Can also be tested manually by editing bootstrap and removing the end of the routing, replaced with:

  $r = new Ushahidi\Storage\Config;
  $a = $r->all('site');
  $s = $r->set('site', 'site_name', 'Lamu:' . rand(1, 9));
  $g = $r->get('site', 'owner_name');
  exit(Debug::Vars($a, $m, $g));

Reviewers: rjmackay

Reviewed By: rjmackay

Subscribers: lkamau, eyedol, dkobia

Maniphest Tasks: T172

Differential Revision: https://phabricator.ushahidi.com/D40