Modified tests to allow testing login & password reset functionality:

- Modify test user adding logic to hash password instead of using pre-hashed password.
- Allow testing environment to be configured via Option values that start w/ 'Tests.'.
- Put a couple test classes into namespaces. Add test event to Piwik\Mail class so emails can be intercepted.
- Change some test logging level to INFO.
- Added load + reload methods to PageFacade in capture.js
Refs #4739, adding mocha + chai to tests/lib dir.
Refs #4739, remove unneeded persist_fixture_data.
Refs #4739, #4189, remove persist_fixture_data config option code, placed OmniFixture into a namespace, removed PHP screenshot testcase classes and added fixture for use w/ JavaScript screenshot tests.