Debugger: Rework Python Debugger

The (re-)enables basic stepping, data display, frame selection etc
for Python 2 and 3. Arguments passing, jump to line etc.
don't work yet.

Change-Id: I8af03e5905092360eb268ba3081a1236b1f8577f
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/debuggerengine.h

@@ -110,6 +110,10 @@ public:
     QString projectSourceDirectory;
     QStringList projectSourceFiles;
 
+    // Used by Script debugging
+    QString interpreter;
+    QString mainScript;
+
     // Used by AttachCrashedExternal.
     QString crashParameter;