Import/Export support into Painless Lab

[stu-elastic]

We can make support easier and facilitate collaboration in Painless Lab by adding an import/export functionality.

Imagine an user is having an issue with a script. Instead of copy and pasting the script into discuss, they can export it (with the appropriate context, params, potentially even mappings, etc) and post that in discuss.

This avoids formatting errors and will allow developers to work on the user's issue with much less friction.

Beyond support issues, painless users can use the mechanism to collaborate amongst themselves, passing exports back and forth. This would be a very nice step toward a robust script development environment in kibana.

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)

[alisonelizabeth]

Closing for now, as this is not a priority at the moment.