List of "all fields" should be confined to all fields of current search result

### Problem description

When clicking on the "all fields" link of the "List fields of current page or all fields" footnote in the fields panel, all fields of all Graylog indices of the entire ES cluster show up every time. IMHO, it would be more intuitive (and more useable) if the fields panel only showed the fields (of all pages) that were contained in the result of the current search after clicking "all fields".

To make my point clear, imagine a user inspecting log messages from a certain stream. Clicking "all fields", the user would expect to see all fields for that particular stream rather than all fields including fields of messages from all the other streams.
### Steps to reproduce the problem
1. Search for a subset of log messages (having a subset of all fields).
2. Click on "all fields" in the fields panel.
### Environment
- Graylog Version: 1.3.3
- Elasticsearch Version: 1.7.4
- MongoDB Version: 3.2.1
- Operating System: SLES 11