Tooltips for notification area icons

[rozniak]

There is some issue with tooltips not displaying for the notification area items on the taskband. I'm not sure if this is something I'm missing or a bug in GTK3. I did some minor testing for this as part of #265 and confirmed that I don't think it's my usage.

I have tried setting the tooltip on the GtkEventBox for the icons, and even tried setting a tooltip on the clock to no avail. I have confirmed that query-tooltip signal is fired by simply logging it out, and the relative co-ords are correct, so it's as if it does try to do something with the tooltip.

I confirmed that GtkLabel should work with a tooltip without any event box faffing by setting a tooltip on the wintc-hello program's label. So the clock should've worked.

Next step is to perhaps check if this is an issue perhaps to do with the notification area being on the edge of the screen? Turn the taskband back into a floating window and see what happens - if tooltips display then this is potentially an upstream GTK3 bug in that it does not display a tooltip when there's definitely space available for one.