[DOCS][Developer] Adopt a top-down approach

Minor corrections to the overview

docs/developer/src/SUMMARY.md

@@ -1,6 +1,5 @@
 # Summary
 
-- [High level view](./high_level.md)
 - [Architecture: Modules](./architecture.md)
     - [Programming Style](./paradigms.md)
     - [Events](./events.md)
@@ -17,7 +16,21 @@
 - [Plugins](./plugins.md)
     - [Configuration](./plugins/configuration.md)
     - [Initialization and Clean Up](./plugins/lifetime.md)
+- [Debugging](./debugging.md)
 - [Sample Plugins](./sample_plugins.md)
     - [Injecting Javascript](plugins/sample_plugins/Awesomeness.md)
     - [Creating a block on the sidebar](plugins/sample_plugins/Sample.md)
 - [Components](./components.md)
+- [Core](./core.md)
+    - [Overview](./core/overview.md)
+    - [Modules](./core/modules.md)
+    - [Event dispatcher](./core/event-dispatcher.md)
+    - [ORM and Caching](./core/orm_and_caching.md)
+    - [Interfaces](./core/interfaces.md)
+    - [UI](./core/ui.md)
+    - [Internationalization](./core/internationalization.md)
+    - [Utils](./core/util.md)
+    - [Queues](./core/queues.md)
+    - [Files](./core/files.md)
+    - [Security](./core/security.md)
+    - [HTTP Client](./core/http.md)