Merge dev to master for Release V0.2.0

[wild-flame]

According to issue https://github.com/nginyc/rafiki/issues/166

consists of PRs: #163 #161 #158 #152 #148 #142 #140 #138

• Refractor Web Admin with new UI
• Allow use of GPU for inference jobs
• Use colour images for IMAGE_CLASSIFICATION
• using kafka to transfer inference worker and predictor infomation
• Update model tuning for regression tasks and add new models
• Add support for tabular dataset and new models (Updated)
• add license to files
• Add support for tabular dataset and new models
• Add docs for speech recognition
• Add Speech Recognition model
• Add architecture tuning with ENAS & hyperparameter tuning with parameter sharing
• Change environment variable check method
• Add new models to Rafiki