Stricter argument validation, parameter cleanup

[28mm]

Stricter Argument Validation:

1. For IBM/Watson, --celebrities entails --faces but should only print celebrity-matched faces.
2. For Microsoft --celebrities entails --categories (not --faces)
3. ...

Parameter Cleanup:

1. Instead of --provider {google,microsoft,amazon,opencv,watson,clarifai,facebook, or in addition to it, it should be possible to specify providers with a single argument, e.g. --google or --microsoft.
2. Ditto output modes: --output {json,yaml,tabular} which would become --json, --yaml, and --tabular.