Run specific features from the CLI

[oh-wo]

• Add functionality similar to the "run file" button in the web UI
• Useful for debugging a single feature file against a developer's local environment (rather than running the entire suite)
• Suggested syntax: obehave test --feature <feature-name>
• Later we might add: obehave test --feature <feature-name> --scenario <scenario-name>. The CLI should throw an error if a scenario is passed without a feature (scenario names are feature scoped?)