Wizard makes editing Event Definitions more complicated

When user only wants to correct some values of an Event Definition, they are presented with a wizard, which requires them to edit, go to the summary step and save the changes.

## Expected Behavior
Editing an Event Definition should not require going through multiple steps.

## Current Behavior
Editing an Event Definition requires to go at least through two steps.

## Your Environment
* Graylog Version: Graylog-3.1.0-rc.3-SNAPSHOT
* Elasticsearch Version:
* MongoDB Version:
* Operating System:
* Browser version: