Switch to Aura.Di and fix config repo, fixes T198

Summary:
- replace Pimple with Aura.Di
- add more comments and clean up init file
- relocate the config repo properly, in the app

Refs D84.

Test Plan:
  ./bin/behat --config application/tests/behat.yml application/tests/features/api.config.feature --format progress

Reviewers: rjmackay, dkobia

Reviewed By: dkobia

Subscribers: lkamau, eyedol

Maniphest Tasks: T198

Differential Revision: https://phabricator.ushahidi.com/D88