Conf Editor update with new Retriever syntax

Updates the to_edit.json file as well as the confEditorCtrl with the recent changes made in #81.

#81 changed the design of retrievers.

Retrievers are not a top main section anymore. Therefore the arrays in plugins that specify retrievers are also gone.
This wasn't a good idea in the first place - in fact, when designing the confEditor this was an area of concern and this appeared to be valid.

The way it was done before didn't allow for retrievers to be reusable.

The diff plugin revealed such a use case, because it also wants to take a treebankRetriever, however configured with a different resource.
The markup of retrievers has therefore changed and is an object again, as in:
```
{ 
  "retrievers" : {
    "TreebankRetrievers" : {
      "resource" : "resourceName"
    }
  }
}
```

Resources are still handled as something like variables.

Reusability of retrievers also lead to a change in their service/factory strucute. It appeared that angular factories are singletons as well. A retriever now should return a constructor function.
Plugins that take retrievers aren't really affected by this change. The handling of a new retriever resource is managed inside the configurator. `configurator.getRetrievers(retrieversObject)` fetches them.