Styling and GTK3

[TeofilC]

As part of #137, the move to GTK3, we had to switch away from some functions we were using to draw styled boxes. They no longer exist in GTK3. So, I have instead just draw some boxes with with Cairo. These don't necessarily match the styling of the current GTK theme. This isn't a huge problem, but depending on your theme, things might look a bit odd.

It would be great if someone could figure out how to restore getting the styles from the theme.

ThreadScope/GUI/EventsView.hs

Lines 308 to 312 in 292a329

	renderWithDrawWindow win $ do
	-- TODO: figure out how I can grab the correct color from GTK's style
	setSourceRGBA 0.2 1 1 0.2
	rectangle 0 y (fromIntegral width) lineHeight
	fill