Switch to a single root namespace for all of Ushahidi, refs T846

Summary:
- switch from PSR-0 to PSR-4
- update namespaces:
  - `Ushahidi` -> `Ushahidi\Core`
  - `UshahidiApi` -> `Ushahidi\Api`
  - `Ushahidi\Factory` -> `Ushahidi\Factory` (out of `Core`)
- update to phpspec 2.1 for PSR-4 support
- update tests as necessary

Test Plan:
```
composer install
bin/phpspec run
bin/behat -c application/tests/behat.yml -f progress
```

to revert back after testing:

```
composer install
```

Reviewers: vladimir, aMoniker

Reviewed By: aMoniker

Subscribers: dkobia, srutto, rjmackay

Maniphest Tasks: T846

Differential Revision: https://phabricator.ushahidi.com/D480