Refactored member controller to use model layer

refs TryGhost/Members#105

- As members module has become a core part it makes sense to follow the same principles as in all other controllers and use the model directly instead of calling external services.
- Bumped @tryghost/members-api to 0.11.1 . New stripe-specific methods used in controllers are available starting with this version
- Exposing these new methods is a little hacky because there are no relationships setup on members_* tables. Left notes for future improvements once relations are introduced.
- We don't allow for chaging member's emails at the moment. For this reason had to modify JSON schema a little. It doesn't support OO inheritence: "This shortcoming is perhaps one of the biggest surprises of the combining operations in JSON schema: it does not behave like inheritance in an object-oriented language. " (ref. https://json-schema.org/understanding-json-schema/reference/combining.html#allof)

packages/admin-api-schema-historic/canary/members-edit.json

@@ -13,7 +13,40 @@
             "maxItems": 1,
             "items": {
                 "type": "object",
-                "allOf": [{"$ref": "members#/definitions/member"}]
+                "additionalProperties": false,
+            "properties": {
+                "name": {
+                    "type": "string",
+                    "maxLength": 191,
+                    "pattern": "^([^,]|$)"
+                },
+                "note": {
+                    "type": "string",
+                    "minLength": 0,
+                    "maxLength": 2000
+                },
+                "subscribed": {
+                    "type": "boolean"
+                },
+                "id": {
+                    "strip": true
+                },
+                "email": {
+                    "strip": true
+                },
+                "created_at": {
+                    "strip": true
+                },
+                "created_by": {
+                    "strip": true
+                },
+                "updated_at": {
+                    "strip": true
+                },
+                "updated_by": {
+                    "strip": true
+                }
+            }
             }
         }
     },