move wellKnownJson to domains

after some more thought:
* If app moves to another location, user has to remember to move all this config
* It's not really associated with an app. It's to do with the domain info
* We can put some hints in the UI if app is missing.

part of #703

src/test/updatechecker-test.js

@@ -41,7 +41,8 @@ const DOMAIN_0 = {
     config: {},
     provider: 'manual',
     fallbackCertificate: null,
-    tlsConfig: { provider: 'fallback' }
+    tlsConfig: { provider: 'fallback' },
+    wellKnown: null
 };
 
 var AUDIT_SOURCE = {