app: remove JSON based schema, and each App returns single namespace

Change-Id: I2ced82edd1251edc592f7ae0156d5ea3c81865c2
diff --git a/core/installer/app.go b/core/installer/app.go
index 611318d..35c6d11 100644
--- a/core/installer/app.go
+++ b/core/installer/app.go
@@ -328,7 +328,7 @@
 	Description() string
 	Icon() template.HTML
 	Schema() Schema
-	Namespaces() []string
+	Namespace() string
 	Render(derived Derived) (Rendered, error)
 }
 
@@ -386,8 +386,8 @@
 	return a.schema
 }
 
-func (a cueApp) Namespaces() []string {
-	return []string{a.namespace}
+func (a cueApp) Namespace() string {
+	return a.namespace
 }
 
 type PortForward struct {