Menas API: replace arrays with objects as top-level JSON reponses

[dk1844]

Background

As outlined in #1597 (comment), Menas API contains top-level arrays in response payloads in a number of endpoints. For reasons outline in the lined discussion, these should be replaced by wrapper objects.

API calls in question:

• /api/properties/datasets
• /api/runs/{summaries, {datasetName}, grouped, /grouped/{datasetName}, /{datasetName}/{datasetVersion}}
• <? extends VersionedModelController>/{list, searchSuggestions, /allVersions/{name}}

Feature

There should be an (extensible) object as a response in JSON.

Example

GET /api/properties/datasets now yields:

[
    {
        "name": "datasetProperty1",
        ...
    },
    {
        "name": "datasetProperty2",
        ...
    }
]

The intended response should be e.g.:

{
    "propertyDefinitions" : [
        {
          "name": "datasetProperty1",
          ...
        },
        {
          "name": "datasetProperty2",
          ...
        }
    ]
}