libgpaste-applet: override menushell stuff

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: rename

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: more async calls

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>