[ZEPPELIN-550] Let interpreter define function for angular js

[Leemoonsoo]

What is this PR for?

This allow interpreter define a function that callable from front-end.

What type of PR is it?

Feature

Todos

• - implement AngularFunction
• - add tests
• - add docs

Is there a relevant Jira issue?

https://issues.apache.org/jira/browse/ZEPPELIN-550

How should this be tested?

Check screenshot

Screenshots (if appropriate)

Questions:

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

[corneadoug]

@Leemoonsoo Closed?

[Leemoonsoo]

This PR is fully functioning with test and docs. However, i think #591 provides much simpler way to use angular display system.
While this PR still adds some complexity into the code base, i'd like to not merge this code.
What do you think?

[corneadoug]

@Leemoonsoo I think #591 is easier indeed.
Just asking in case closing it was a mistake :)