Tracking Vision Development. #2753

There are some things missing in vision that should be added to complete the service.

• Add support for image = client.image(filename='./my.jpg'). (Add loading image from filename. #2778, Add filename parameter to client image proxy. #2792)
• Make public method for multiple annotation detection(Add image.detect() for detecting multiple types. #2770).
• Move emotion attributes directly to face. face.joy instead of face.emotions.joy. (Move emotions to Face class. #2782)
• Add system tests Add Vision system tests #2526. (Add system test for Vision Logo detection. #2788, Add system tests for detect_faces(). #2827, Add vision detect_labels() system tests. #2830, Add Vision detect_landmarks() system tests. #2834, Add Vision system tests for detect_safe_search(). #2835, Add Vision detect_text() system tests. #2836, Add Vision detect_properties() system tests. #2839)
• Add GAPIC support. (Add Vision Image and Feature gRPC conversion helper functions. #2914, Add gax support for entity annotations. #2918, Vision: Add gRPC support for face detection. #2922, Vision: Add gRPC support for image properties. #2937, Vision: Add gRPC support for safe search. #2938)
• Add batch processing, annotation multiple images with one request.(Adding batch image processing to Vision API #2897, Vision support for batch processing part one. #2967, Vision: Add batch processing #2978)
• Rename Face.Landmark to something like Face.FacialFeature(Update reference to bounds. #2833 (comment)).
• Move snippets to docs/vision_snippets.py.
• Add more examples and update documentation(Cleaning up docs and fixing typos #2754).
• Refactor unit tests.