Send 500 responses for real interceptor activation errors

Shouldn't affect the UI significantly AFAICT but this does make it
easier to debug these particularly when scanning through the network
traffic (and of course, it's just the right RESTy thing to do)

Author: pimterry

src/api/api-model.ts

@@ -199,7 +199,7 @@ export class ApiModel {
                         code: activationError.code,
                         message: activationError.message
                     }
-                    : {}
+                    : false
             };
         }
     }

src/api/rest-api.ts

@@ -73,7 +73,13 @@ export function exposeRestAPI(
 
         const interceptorOptions = req.body;
         const result = await apiModel.activateInterceptor(interceptorId, proxyPort, interceptorOptions);
-        res.send({ result });
+
+        if (result.success === true || result.error === false) {
+            // Some non-success is just temporary, e.g. global Chrome "exit running app please" confirmation.
+            res.json({ result });
+        } else {
+            res.status(500).json({ result });
+        }
     }));
 
     server.post('/client/send', handleErrors(async (req, res) => {