Instead, it should enter the world fully formed.

Primarily, this rearranges how listeners are handled internally by the
various PerformanceView classes so that there's not so much redundancy.

It also fixes ReversePerformance and ProxyPerformance to not leak.
Previously, they never unhooked their listeners, so they'd leak until
the entire chain of performances was killed. Now, they unhook as soon as
they themselves have no listeners left, which is more idiomatic.

Instead of separate functions for the 0->1 and 1->2 transitions, just
have one function.

One might argue, the most basic utility classes.

So you don't fade out when going to a popup menu, for example.

For those times when you want to do something as you move away from a
route into the next one, as well as when you move into it from the
previous one.