Modify LogFile to open/close file on SD card status.

Previously, would only open on construction, which was only when the receiver mode changed, which wasn't all that useful.

firmware/application/ais_app.hpp

@@ -98,12 +98,10 @@ private:
 
 class AISLogger {
 public:
-	AISLogger();
-
 	void on_packet(const ais::Packet& packet);
 
 private:
-	LogFile log_file;
+	LogFile log_file { "ais.txt" };
 };
 
 namespace ui {