gtk-demo: Replace old code

gtk-demo: Replace old code

"Hey I know, let's do an easter egg!"
"What kind of easter egg?"
"We can nest lots of textviews!"
"Sounds cool!"
...
"But how does one see a textview inside a textview?"
"What do you mean?"
"Well, it just looks like black text on a white background."
"You mean it's the same as if we just duplicated the text?"
"Yeah!"
"Hrm, maybe we can put a frame around it."
"Sounds good. I'll stuff the textviews in a GtkFrame."
"What? Why? Let's use a GtkEventBox and override its background"
"Why is that a good idea when we have GtkFrame?"
"Because I said so!"
"Okay."