/stac/collections api returns blank response when supportCollections=false

[mhogeweg]

when the setting supportsCollections is set to false in app-context.xml, the STAC /stac/collections API responds with HTTP 200 but has an empty response body. This does not happen when supportsCollections="true".

in this situation, the request to individual collections /stac/collections/{collectionId} still responds as expected.

[mhogeweg]

resolved in branch Stac_Fixes