added control sidebar #10 (#87)

- added configurable sidebar #10
- added language switch in sidebar preferences tab #10
- added sidebar tab with kimai beta-info message #10
- use trait for repositories
- improved README

config/packages/avanzu_admin_theme.yml

@@ -9,6 +9,6 @@ avanzu_admin_theme:
         boxed_layout: false
         collapsed_sidebar: true
         mini_sidebar: true
-        control_sidebar: false
+        control_sidebar: true
     knp_menu:
         enable: false