Python: make interpreter configurable

Add settings page to setup python interpreter and use a combo box in the
run configuration to switch between those configured interpreter.

Change-Id: I51014b785ea822ee138d39c788149f1d22901e55
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/python/python.pro

@@ -11,10 +11,15 @@ HEADERS += \
     pythonindenter.h \
     pythonformattoken.h \
     pythonscanner.h \
+    pythonsettings.h
 
 SOURCES += \
     pythonplugin.cpp \
     pythoneditor.cpp \
     pythonhighlighter.cpp \
     pythonindenter.cpp \
-    pythonscanner.cpp
+    pythonscanner.cpp \
+    pythonsettings.cpp
+
+RESOURCES += \
+    python.qrc