Allow ADS-B to send airport ATC frequencies to Frequency Scanner.

Add ATC callsigns.
Add ATC mode, displaying basic info for all aircraft.
Add airport range rings.
Change Device setting to be an AM Demod setting, so AM demod isn't at DC.
Add basic aircraft data to ADSB Web API report.

sdrbase/maincore.cpp

@@ -433,3 +433,20 @@ void MainCore::updateWakeLock()
 }
 #endif
 
+std::vector<ChannelAPI*> MainCore::getChannels(const QString& uri)
+{
+    std::vector<ChannelAPI*> channels;
+
+    for (const auto deviceSet : m_deviceSets)
+    {
+        for (int chi = 0; chi < deviceSet->getNumberOfChannels(); chi++)
+        {
+            ChannelAPI* channel = deviceSet->getChannelAt(chi);
+            if (channel->getURI() == uri) {
+                channels.push_back(channel);
+            }
+        }
+    }
+
+    return channels;
+}