user should be able to export view and import in different system

## Expected Behavior
As user with access to multiple Graylog environments you want to move your created view between the environments. While that might be possible for the admin making use of the content packs a user should also be able to make this. Similar to what Grafana provides (show json of dashboard, import json of dashboard).

## Context
If you are in a restrictive environment with only limited admins but endless users that are accessing multiple environments it is painful to make use of the views in different environments (staging, dev, prod) as you need to create that view and all additional settings and changes in all environments.

As user with limited priviledges you can't use the content pack feature for that so it would be helpful to export/import json.

## Your Environment

* Graylog Version: 3.1