feat: implement the base classes for launcher + input

- Base classes for lancher: Dashboard + Taskbar
- Allow the shell to monitor directly wayland seat keyboard (on demand)

resources/gresource-session.xml

@@ -4,5 +4,7 @@
             <file alias="dev.iohub.diya.session-shell.css">resources/session-shell.css</file>
             <file alias="virtual-keyboard.css">resources/virtual-keyboard.css</file>
             <file alias="default.keymap">resources/default.keymap</file>
+            <file alias="dashboard.ui">resources/ui/dashboard.ui</file>
+            <file alias="taskbar.ui">resources/ui/taskbar.ui</file>
     </gresource>
 </gresources>