multimedia/w_scan2: add working fork of expiring multimedia/w_scan

w_scan2 is a small channel scan tool which generates ATSC, DVB-C,
DVB-S/S2 and DVB-T/T2 channels.conf files.

It's based on the old "scan" tool from linuxtv-dvb-apps-1.1.0. The
differences are:

• no initial tuning data needed, because scanning without this data is exactly what a scan tool like this should do.
• it detects automatically which DVB/ATSC card to use.
• much more output formats, interfacing to other dtv software.

w_scan2 is a fork of the original w_scan from
https://www.gen2vdr.de/wirbel/w_scan/index2.html

Main changes from w_scan to w_scan2:

• keep duplicate transponders by default because a stronger transponder with the same ID might have a higher frequency and be discarded simply because it's scanned later. Also don't replace the current transponder with an advertised one by default. The latter may have a lower signal strength. More details here: https://stefantalpalaru.wordpress.com/2016/02/04/scan-all-the-things/ The old behaviour can be enabled with -d (--delete-duplicate-transponders).
• re-enable VHF band III in Europe

WWW: https://github.com/stefantalpalaru/w_scan2

Suggested by: hselasky