Improved project file structure

tests/custom/database/src/main.py

@@ -0,0 +1,14 @@
+from cpl_core.application import ApplicationBuilder
+
+from application import Application
+from startup import Startup
+
+
+def main():
+    app_builder = ApplicationBuilder(Application)
+    app_builder.use_startup(Startup)
+    app_builder.build().run()
+
+
+if __name__ == '__main__':
+    main()