default.js

This mimics default.src very closely, even the curious clear-screens before
the menu displays only when in non-expert mode (?).

I'll likely be using this to recreate some other command shells.

There's a couple of RIP-specific calls to getlines in default.src that I did
not port over (yet).

This commit fixes issue #526 for Nelgin (and any other JavaScript devs).

Note: this file supercedes default.bin, so beware if you have customized
default.src (and built your own custom default.bin), you'll want to move
those to your mods directory to continue to use them.

Another nail in Baja's coffin.