Redirect Qt messages to sqlite log mechanism

In Windows (related issue #1069) and maybe in macOS (related issue #1982)
output to console is inhibited.

This will allow these messages to be seen in our Error Log window.

src/main.cpp

@@ -1,7 +1,23 @@
 #include "Application.h"
+#include "sqlite.h"
+
+void db4sMessageOutput(QtMsgType type, const QMessageLogContext &, const QString &msg)
+{
+    QByteArray localMsg = msg.toLocal8Bit();
+
+    // Emulate the default Qt treatment. This might not work in some OS, like Windows.
+    fprintf(stderr, "%s\n", localMsg.constData());
+
+    // Log using the SQLite log mechanism, so it gets the same treatment than messages
+    // reported by SQLite itself. This will allow these messages to be seen in our Log window.
+    // Error code will be the type
+    sqlite3_log(static_cast<int>(type), "%s\n", localMsg.constData());
+}
 
 int main( int argc, char ** argv )
 {
+    qInstallMessageHandler(db4sMessageOutput);
+
     // Create application object. All the initialisation stuff happens in there
     Application a(argc, argv);