[adv_windowlist] navigation keys as in vim

It would be great if you could navigate the channel list in AWL with keyboard shortcuts (ex: when all the channels you are joined to are no longer visible in the screen view), in a similar way to how it can be done with the `tmux-nicklist-portable.pl` script.

For example:
```
k/up arrow: up one line
j/down arrow: down one line
u/pageup: up 50% lines
d/pagedown: down 50% lines
gg: go to top
G: go to bottom
```