Registry - 0.3.0 release

• SchemaRegistry HA Support
• Changes to SchemaRegistryClient, made id & version in messages optional
• ML Registry module
• SECURITY, SPNEGO Auth for REST APIs
• Handling Null values
• Improvements to Wire protocol
• Key/Value suffix customization for Avro SerDes
• Versioned Entities, can be used to build other registry services
• Search API in finding schemas with name, description
• UI Improvements
• Postgres as storage support
• Optional Schema Evolution
• UI Bug fixes
• Code refactoring & Bug fixes