Clean up some names (rename classes, methods, files)

* ConvenienceClasses.h/.inl/.cpp -> ConvenienceApiClasses.h/.inl/.cpp
  * IObjectProxy class -> IProxy
  * Interfaces class -> AdaptorInterfaces
  * Interfaces.h -> split into AdaptorInterfaces.h and ProxyInterfaces.h
  * createObjectProxy() method -> createProxy()

include/sdbus-c++/Error.h

@@ -1,7 +1,7 @@
 /**
  * (C) 2017 KISTLER INSTRUMENTE AG, Winterthur, Switzerland
  *
- * @file ConvenienceClasses.h
+ * @file Error.h
  *
  * Created on: Nov 8, 2016
  * Project: sdbus-c++