gpaste-settings: rewrite in C

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

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

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

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