ncurses: lot of changes stacked together

- remove some messages logging dead code
- don't store the ncurses WINDOW, use global stdscr instead
- add some fancy unicode characters to the help
- factorize list navigation key handling
    all boxes now use the same code than PLAYLIST/BROWSE
    this means there is now a selector in every box
- break Redraw() in several functions
- remove fancy characters from Status box drawing code
    use the same layout than meta-info / info boxes
- fix a display bug in objects box
- simplify some functions and remove unneeded arguments
- avoid a strdup() in ReadDir() loop

        Known regressions:
- when switching back to PLAYLIST box, the selector will be set to the
  playing item only after the 2nd refresh (i.e. maximum 1 second later)