Refactor common code into helper function
Refactor common code into helper function

Refactor-out setting and getting ArrayOfStringsType properties. Those
properties always map to std::vector<std::string>.

otris/ews-cpp,m-Schlitzer/ews-cpp,m-Schlitzer/ews-cpp,otris/ews-cpp,m-Schlitzer/ews-cpp,otris/ews-cpp,bkircher/ews-cpp,bkircher/ews-cpp,otris/ews-cpp,bkircher/ews-cpp