Update deprecated GTK calls

[Ross Younger]

There are a number of these, which need to be worked through and squashed.

[Ross Younger (crazyscot)]

Existing comments reveal:

 * replace gtk_signal_connect() with g_signal_connect()
 * convert to use cairo
 * use GtkUIManager instead of GtkItemFactory

[Ross Younger (crazyscot)]

Really ought to squash all GTK assertions. There's (currently) one coming off the About box.

[Ross Younger (crazyscot)]

Regarding cairo, I should go read http://www.cairographics.org/documentation/ - particularly its tutorial.
cairo_image_surface_create_for_data is probably the one that I'm looking for for the main canvas.

[Ross Younger (crazyscot)]

There's an entry in the FAQ about using pango with cairo - this will cover the HUD. I could presumably put the HUD on its own layer, switch the layer on and off rather than rerendering - even move it around at will. This will probably turn into another feature request.