Base/App: add new signal interface to Parameter

Added new signal interface using boost::signals2 signalParamChanged.

Exposed to Python as ParameterGrpPy.AttachManager() to monitor changes
to all parameters, sub groups under the referring group.

Added new attribute for ParameterGrp(Py) to query the Parent and Manager
of the referring group.

src/Base/Handle.cpp

@@ -64,6 +64,13 @@ void Handled::unref() const
     }
 }
 
+int Handled::unrefNoDelete() const
+{
+    int res = _lRefCount->deref();
+    assert(res>=0);
+    return res;
+}
+
 int Handled::getRefCount() const
 {
     return static_cast<int>(*_lRefCount);