Lint: fix several issues discovered by clang-tidy

src/App/PropertyContainer.h

@@ -296,7 +296,7 @@ private: \
   TYPESYSTEM_HEADER_WITH_OVERRIDE(); \
 protected: \
   static const App::PropertyData * getPropertyDataPtr(void); \
-  virtual const App::PropertyData &getPropertyData(void) const override; \
+  const App::PropertyData &getPropertyData(void) const override; \
 private: \
   static App::PropertyData propertyData
 ///

src/Base/Parameter.cpp

@@ -151,7 +151,7 @@ public:
     void resetErrors() {}
 
     /* Unimplemented constructors and operators */
-    DOMPrintErrorHandler(const DOMErrorHandler&) = delete;
+    explicit DOMPrintErrorHandler(const DOMErrorHandler&) = delete;
     void operator=(const DOMErrorHandler&) = delete;
 
 };