Misc. typos

- Tooltip uniformity 
- source comment typo fixes
- remove double whitespaces

src/App/DocumentObjectExtension.h

@@ -48,7 +48,7 @@ public:
     App::DocumentObject*       getExtendedObject();
     const App::DocumentObject* getExtendedObject() const;
   
-    //override if execution is nesseccary
+    //override if execution is necessary
     virtual short extensionMustExecute(void);
     virtual App::DocumentObjectExecReturn *extensionExecute(void);
     

src/App/Extension.h

@@ -63,7 +63,7 @@ void * _class_::create(void){\
    return new _class_ ();\
 }
 
-/// define to implement a  subclass of Base::BaseClass
+/// define to implement a subclass of Base::BaseClass
 #define EXTENSION_TYPESYSTEM_SOURCE_ABSTRACT_P(_class_) \
 Base::Type _class_::getExtensionClassTypeId(void) { return _class_::classTypeId; } \
 Base::Type _class_::getExtensionTypeId(void) const { return _class_::classTypeId; } \
@@ -155,7 +155,7 @@ template<> void _class_::init(void){\
  * The special python extension type created above is important, as only those python extensions 
  * can be added to an object from python. It does not work to add the c++ version directly there. 
  * 
- * Note that every method of the extension becomes part of the extendded object when added from c++. 
+ * Note that every method of the extension becomes part of the extended object when added from c++. 
  * This means one should carefully design the API and make only necessary methods public or protected.
  * Every internal method should be private.
  * 
@@ -210,7 +210,7 @@ template<> void _class_::init(void){\
  * };
  * @endcode
  * @Note As seen in the code there are multiple helper macros to ease the repetitive work of querying 
- * and calling methods of the proxy object. See the maco documentation for howto use them.
+ * and calling methods of the proxy object. See the macro documentation for how to use them.
  * 
  * To ensure that your wrapper is used when a extension is created from python the extension type must 
  * be exposed as follows:
@@ -218,8 +218,8 @@ template<> void _class_::init(void){\
  * typedef ExtensionPythonT<MyExtensionPythonT<MyExtension>> MyExtensionPython;
  * @endcode
  * 
- * This boilerplate is absolutely nesseccary to allow overridable methods in python and it is the 
- * exension creators responsibility to ensure full implementation.
+ * This boilerplate is absolutely necessary to allow overridable methods in python and it is the 
+ * extension creator's responsibility to ensure full implementation.
  * 
  */
 class AppExport Extension
@@ -315,8 +315,8 @@ private:
   
 
 /**
- * Generic Python extension class which allows to behave every extension
- * derived class as Python extension -- simply by subclassing.
+ * Generic Python extension class which allows every extension derived
+ * class to behave as a Python extension -- simply by subclassing.
  */
 template <class ExtensionT>
 class ExtensionPythonT : public ExtensionT