about; update date

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: mark application allow-none

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: don't close on delete

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