airodump-ng: refactor displaying of STATIONs

[gemesa]

Did some refactoring in airodump-ng, this way the code can be extended easier if we want to add additional - variable length - columns. Main difference is that I replaced printf() with snprintf() so It is also consistent with the rest of the code.
This is a preparation for implementing #2167. I think that feature is a good idea and also got some attention by other users so I will reimplement it. That implementation has some bugs though, like the empty lines and does not handle the case properly if the manufacturer string is longer than 32 characters.

Fixed some indentation issues also in the displaying of stations.

Before:

$ sudo airodump-ng wlp0s20f0u1
 BSSID              STATION            PWR   Rate    Lost    Frames  Notes  Probes

 XX:XX:XX:XX:XX:XX  XX:XX:XX:XX:XX:XX  -55    0 - 6      0        1

As you can see Rate and Lost column titles are shifted by one space.

After:

$ sudo ./airodump-ng wlp0s20f0u1
 BSSID              STATION            PWR    Rate    Lost   Frames  Notes  Probes

 (not associated)   XX:XX:XX:XX:XX:XX  -87    0 - 1     18        6         XXXXXXXXXX

[gemesa]

Closing for now as I have to make sure the UI keeps working properly. Will review it later.