Python: Initialize settings in the pimpl

Change-Id: I172136851c3002bf785d9b8f378c0cccc408e0e2
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/python/pythonsettings.h

@@ -14,10 +14,9 @@ class PythonSettings : public QObject
     Q_OBJECT
 
 public:
+    PythonSettings();
     ~PythonSettings();
 
-    static void init();
-
     using Interpreter = ProjectExplorer::Interpreter;
 
     static QList<Interpreter> interpreters();
@@ -47,8 +46,6 @@ public slots:
     void listDetectedPython(const QString &detectionSource, QString *logMessage);
 
 private:
-    PythonSettings();
-
     void initFromSettings(QSettings *settings);
     void writeToSettings(QSettings *settings);