Add Wi-Fi Flow Collection support in ntopng

[lucaderi]

As of today

• nProbe collect flows containing Wi-FI information

and exports the SSID name and the MAC address of the sending station - nProbe delivers flows to ntopng that displays them on the flow information page

This ticket is to request to

• Store APN MAC and SSID in Historical Flows
• Implement an SSID page (e.g. similar to the AS page) that displays for each SSID (regardless of the AP MAC address) traffic up/down and a timeseries icon that displays the SSID traffic stats
• Add the SSID drop-down in the report dashboard
  
• Add the ability to search historical flows according to APN MAC and/or SSID