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()

test/perftests/org.sdbuscpp.perftests.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
 <node name="/org/sdbuscpp/perftest">
-    <interface name="org.sdbuscpp.perftest">
+    <interface name="org.sdbuscpp.perftests">
         <method name="sendDataSignals">
             <arg type="u" name="numberOfSignals" direction="in" />
             <arg type="u" name="signalMsgSize" direction="in" />