Editing an extractor should use message loader tabs

When editing an existing extractor for an input, it is showing a sample message for the user to work on. This sample message is currently the most recent one received on the input the extractor is attached to. Alternatively, the user can choose to load a different message, but only manually - based on message id and index.

It should be possible for the user to load yet another message from the input to verify that the extractor works on subsequent messages. Therefore - and for consistency - it should make use of the `LoaderTabs` component, just like the stream rule editor and extractor creation do.