[libcalamares] Un-clog Logging

- Map QtMsgType -- used by qDebug() and qWarning() -- to levels used
  by Calamares in a consistent fashion.
- Drop unused log levels (INFO, EXTRA unused in any Calamares code).

src/libcalamares/utils/Logger.cpp

@@ -33,7 +33,7 @@ static unsigned int s_threshold =
 #ifdef QT_NO_DEBUG
     Logger::LOG_DISABLE;
 #else
-    Logger::LOGEXTRA + 1;  // Comparison is < in log() function
+    Logger::LOGDEBUG;  // Comparison is < in log() function
 #endif
 static QMutex s_mutex;
 
@@ -105,20 +105,21 @@ CalamaresLogHandler( QtMsgType type, const QMessageLogContext&, const QString& m
     const char* message = ba.constData();
 
     QMutexLocker locker( &s_mutex );
+
     switch ( type )
     {
-    case QtDebugMsg:
+    case QtInfoMsg:
         log( message, LOGVERBOSE );
         break;
-
-    case QtInfoMsg:
-        log( message, 1 );
+    case QtDebugMsg:
+        log( message, LOGDEBUG );
         break;
-
-    case QtCriticalMsg:
     case QtWarningMsg:
+        log( message, LOGWARNING );
+        break;
+    case QtCriticalMsg:
     case QtFatalMsg:
-        log( message, 0 );
+        log( message, LOGERROR );
         break;
     }
 }

src/libcalamares/utils/Logger.h

@@ -47,8 +47,6 @@ enum
     LOG_DISABLE = 0,
     LOGERROR = 1,
     LOGWARNING = 2,
-    LOGINFO = 3,
-    LOGEXTRA = 5,
     LOGDEBUG = 6,
     LOGVERBOSE = 8
 };