Display current program name in the browser's status bar

[jmmv]

As of recently, the program-related commands keep track of the currently-loaded program so that the editor can display its name and so that SAVE can reuse it. But, while we are on the REPL, it's impossible to know what program is loaded.

An original thought was to display a status bar within the terminal, similar to the one the editor shows, and mimicking what QBASIC did for DOS. But I'm not sure we should go that way.

For now, though, it should be relatively easy to display this name in the browser's status bar along with the screen size and the like. And let's face it: most people are just going to use the web UI so this might be good enough.