razorqt-panel/panel: Save settings right after the close button clicked

The panel settings are saved in a delayed mode. But... when the user clicks
the Close button the settings should be saved right way. This is useful
for the developer. A developer may kill the panel before the settings are
actually saved and that can confuse the developer.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Merge pull request #639 from luis-pereira/fix-panel-save-config

razorqt-panel/panel: Save settings right after the close button clicked