[Zeppelin-4582] add scala profile 2.12

[redsk]

What is this PR for?

Add scala 2.12 support for interpreters. Based on PR3634

What type of PR is it?

Improvement

Todos

• [ ] - scalate-maven-plugin used in cassandra does not exist for scala 2.12 and has not been in development since 2015. However, there's a version compiled for scala 2.12 here. But no single version compiled for the three scala version (which would be needed for Zeppelin's pom.xml). I've hacked my way like this just to compile Zeppelin but we probably need a better solution.
• [ ] - Beam. beam-runners-flink_2.12 does not exist. There seem to be a workaround but I've not tried it. I've just disabled Beam from the modules for testing Zeppelin.

What is the Jira issue?

https://issues.apache.org/jira/browse/ZEPPELIN-4582

How should this be tested?

Not done yet.

Questions:

• Does the licenses files need update? No
• Is there breaking changes for older versions? Unsure
• Does this needs documentation? Probably

[alexott]

My general question is - do we really need to support multiple versions of Scala globally? Interpreters are better isolated right now from each other & core, so each interpreter can use its own version of Scala. And for some interpreters, like, beam we don't have specific Scala version (I think that I had this problem with Ignite as well).

Maybe it makes sense to start a discussion in dev list about need of the switch between different Scala versions?