WindowManager: fix code for tap action service

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Tests: improve a bit the visual appearance of the DummyWindow, and prepare the field for method registering testing

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Tests: adapt stubs to the new message system (with payload)

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Launcher: add missing launcher background image

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>