libgpaste-applet: pass correct button to menu popup

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

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
ligbpaste-applet: remove FIXME

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: item: use button_release_event

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
ligbpaste-applet: item: add text mode

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: history: add text-mode

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: don't use NULL event

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