[ACA-1619] automatically show content metadata (#1104)

* [ACA-1619] overwrite the app.config metadata settings only of the 'content-metadata-presets' is non-empty

* [ACA-1619] app config to show automatically all metadata aspects

- not extendable version

* [ACA-1619] app extension to show automatically all metadata aspects

- extendable version
- the app.config setting is overwritten by the one with ids from app.extensions
- could remove completely the content metadata setting from app.json

* [ACA-1619] allow 'disabled' property on content metadata configuration

* [ACA-1619] test content-metadata plugin extension

 - allow 'disabled' property on content metadata configuration

* [ACA-1619] remove test reference to metadata plugin

* [ACA-1619] backwards compatibility for metadata plugin extensions

- add back initial structure (& ids) of content-metadata "custom" preset
- revert change to sample metadata extension plugin

* [ACA-1619] forgotten change

* [ACA-1619] tests

extension.schema.json

@@ -371,6 +371,14 @@
         "id": {
           "type": "string",
           "description": "Unique identifier"
+        },
+        "includeAll": {
+          "type": "boolean",
+          "description": "Enable to automatically show all properties"
+        },
+        "disabled": {
+          "description": "Toggles disabled state",
+          "type": "boolean"
         }
       },
       "patternProperties": {
@@ -748,6 +756,10 @@
               "id": {
                 "type": "string",
                 "description": "Unique identifier"
+              },
+              "disabled": {
+                "type": "boolean",
+                "description": "Toggle disabled state"
               }
             },
             "patternProperties": {