Base/App: fix warnings from code analysers:

* convert old-style-casts to explicit C++ casts where possible
* make some implicit conversions explicit

src/Base/GeometryPyCXX.cpp

@@ -127,7 +127,8 @@ Py::Object Vector2dPy::repr()
     Py::Float y(v.y);
     std::stringstream str;
     str << "Vector2 (";
-    str << (std::string)x.repr() << ", "<< (std::string)y.repr();
+    str << static_cast<std::string>(x.repr()) << ", "
+        << static_cast<std::string>(y.repr());
     str << ")";
 
     return Py::String(str.str());