Scala 2.12, Attribute lineage highlighting, MongoDB, ElasticSearch, Cassandra and more

Spline 0.5 comes with a few major improvements and new features:

Spline Agent for Spark (aka Spline Harvester)

1. Agent is now a separate project, located in its own repo
   and loosely coupled with the Spline core via the Producer REST API

2. [#212] Scala 2.12 is supported (for Spark 2.4)

3. Support for some alternative data source types (special thanks to @radford1)

• [#606] ElasticSearch connector support
• [#605] MongoDB connector support
• [#604] Cassandra connector support

Spline Core and UI

• [#112][#559][#451] Attribute lineage and impact highlighting
• [#442] Search by attribute name
• [#616] Support conventional upper snake notation for environment variables
• [#620] ArangoDB SSL connection support
• [#617] ArangoDB fallback config support
• [#615] Connection Performance Improvements (Timeout config, gzip)
• [#561] Docker composite layer for Demo (thanks to @rtyler)

Other improvements and bug fixes

• [#572] Cross-framework end-to-end lineage example
• [#534][#554] Improve logging
• [#635] Client UI WebJar should not have any bytecode dependencies
• [#612] Lineage Timestamp format is misleading
• [#565] Admin CLI doesn't exit normally
• [#535] spark-shell / pyspark --packages not working
• [#629] Missing configuration property spline.consumer.url

...and more