Pool pluggable rebase

[fireboy1919]

What is this PR for?

This is a step towards creating a REST endpoint from resource pools https://issues.apache.org/jira/browse/ZEPPELIN-699

It allows resources to be saved to disk so that they can be reloaded.

What type of PR is it?

Improvement

Todos

• - Add ability to use different kinds of resource pools, and show a second type.

What is the Jira issue?

Partially implements this: https://issues.apache.org/jira/browse/ZEPPELIN-699

Note, that this pull request is dependent upon this one:
#782

How should this be tested?

1. Edit an interpreter
2. Add a new property to the interpreter - the "ResourcePoolClass" - and assign it to "org.apache.zeppelin.resource.VFSResourcePool"
3. Run the interpreter

You should see new resource files created in notebook/zeppelin_resources

Screenshots (if appropriate)

Questions:

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