We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
This is an application analogous to WidgetGallery, in that it tests
various capabilities of LibGUI models. Right now it is pretty bare, but
as more work towards LibGUI models is done regarding persistent model
indices, more demos will be added.
