Ability to create rules with a Graylog query

[frantz45]

When we started this plugin the only possibility to filter logs in an Event Definition were the Streams.
But now Graylog can also use a query.

So when creating a rule with the Wizard we could also be able to set a query in addition to optionnaly use Streams.

[c8y3]

• In the wizard, add a "Search Query" field which corresponds to the "Search Query" of the event definition
• allow the creation of a rule where there is only a Search Query, but no conditions (in which case the Event Definition Streams should be empty)
• allow the creation of a rule with only condition, but no Search Query (like today)
• allow the case where both are configured: the Event Definition Stream is connected to the Stream which carries the conditions