Virtual keyboard + configuration:

- complete implementation of virtual keyboard
- support loading user defined virtual keyboard from configuration at $XDG_CONFIG_HOME/xkb/
- support loading user defined CSS theme from $XDG_CONFIG_HOME/themes/

resources/gresource-session.xml

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gresources>
     <gresource prefix="/dev/iohub/diya/shell">
+            <file alias="dev.iohub.diya.session-shell.css">resources/session-shell.css</file>
             <file alias="default.keymap">resources/default.keymap</file>
     </gresource>
 </gresources>