Properly raise windows on activation

This is a quick PoC to implement the necessary bit of gtk-shell to fix #93 (closed) for window activation (since the upstream protocol discussion seems to take way longer and so we can safe implementing the toolkit part until this is settled in).

Can be desktop on desktop by e.g. lanunching gedit, selecting help form the menu, putting the help window in the background and seleting help again. The functions used there are the same as e.g. when contacts talks to chatty.

This is leaky, i'll clean this up over the next days.

Closes: #93 (closed)