Add .gitignore, .dockerignore and .travis.yml for each feature branch

[aniruddhavpatil]

• [x] feature/data-retrieval
• [x] feature/post-processing
• [x] feature/message-handler
• [x] feature/api-gateway
• [x] feature/user-management
• [x] feature/session-management
• [x] feature/user-interface

[nbafna04]

Created