window registry about chipper8

[fokoid]

Doesn't look like the Pythonic approach can be reasonably achieved in Rust due to lack of runtime introspection. So the new idea is a trait and a hard coded vector of windows.

This was easy enough for everything except the repl window. This one has a different signature for its ui() method since it takes a mutable reference to the command buffer. Once the input field is moved to the bottom bar in #41 this shouldn't be a problem.

[fokoid]

Actually it's still a problem. It was necessary and made sense to move the history buffer out of the UI since it's really application state, not UI. (If we didn't do this then command executions in the main application needed to interact with GUI code to update the history hidden inside the GUI structs.)

But now this means that the command history must be passed to the REPL history UI, so it still has a different signature to the rest. I'm going to leave this for now. After all, it is fundamentally different to other UI elements, since it shows application state whereas all the others show only machine state.