editor: move invalidation to helpers

Make it look like Qt to keep things simpler
editor: use socket_poll-helper
editor: create a helper to set statusbar-text
editor: drop custom window events
editor: wrap up current-value dirtying
editor: wrap and merge row/track changed events
editor: clean up input
editor: clean up statusbar-updates
editor: fix member initialization order
editor: fix int/size_t mismatch

As the editor currently only builds on 32-bit Windows, this is not
a real-world problem, as int and size_t are the same size.

However, this is about to change...
editor: port to Qt
editor: only invalidate tracks if edit-track changed