LastDPActionTime added to output (#52)

Enhancement for #47 / #48: LastDPActionTime() gives back last event on datapoint.
For compatibility I did not replace the function call of `timestamp=...`, but added new `lastdpactiontime=....` output

Co-authored-by: Jens Maus <mail@jens-maus.de>

xmlapi/state.cgi

@@ -114,6 +114,7 @@ if {[info exists sid] && [check_session $sid]} {
                     Write("' valuetype='" # oDP.ValueType());
                     Write("' valueunit='" # oDP.ValueUnit());
                     Write("' timestamp='" # oDP.Timestamp().ToInteger());
+                    Write("' lastdpactiontime='" # oDP.LastDPActionTime().ToInteger());
                     Write("' />");
                   }
                 }
@@ -133,4 +134,4 @@ if {[info exists sid] && [check_session $sid]} {
 } else {
   puts -nonewline {<not_authenticated/>}
 }
-puts "</state>"
+puts "</state>"