Add GMSK, fix modem bandwidth logic, cleanup.

src/modules/modem/analog/ModemAM.cpp

@@ -4,6 +4,10 @@ ModemAM::ModemAM() : ModemAnalog() {
     demodAM = ampmodem_create(0.5, 0.0, LIQUID_AMPMODEM_DSB, 0);
 }
 
+ModemAM::~ModemAM() {
+    ampmodem_destroy(demodAM);
+}
+
 Modem *ModemAM::factory() {
     return new ModemAM;
 }
@@ -12,6 +16,10 @@ std::string ModemAM::getName() {
     return "AM";
 }
 
+int ModemAM::getDefaultSampleRate() {
+    return 6000;
+}
+
 void ModemAM::demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *audioOut) {
     ModemKitAnalog *amkit = (ModemKitAnalog *)kit;