Improved temperature reporting for Drude particles (#3486)

* DrudeLangevinIntegrator has getSystemTemperature()

* DrudeNoseHooverIntegrator has getSystemTemperature()

* StateDataReporter reports system temperature for Drude systems

* Fixed incorrect return type

wrappers/python/src/swig_doxygen/swigInputConfig.py

@@ -225,6 +225,7 @@ UNITS = {
 ("*", "getNonbondedMethod") : (None, ()),
 ("*", "getGlobalParameterDefaultValue") : (None, ()),
 ("*", "getPermutationMode") : (None, ()),
+("*", "computeSystemTemperature") : ("unit.kelvin", ()),
 ("LocalCoordinatesSite", "getOriginWeights") : (None, ()),
 ("LocalCoordinatesSite", "getXWeights") : (None, ()),
 ("LocalCoordinatesSite", "getYWeights") : (None, ()),