Improved Change Passwd by adding Gateway Passwd

Hi there, I've improved on the change password feature of Remmina. I've added the ability to also change the Gateway Password in mass. I don't know if this has ever been requested but for me it is an essential feature since I use Remmina for a professional purpose and of course my password changes every so often. And since I use a RD Gateway to connect to Windows servers changing my Gateway password had become a chore. I've haven't created any translations for the new labels. I'll be happy to do it for languages I know. Thank you. FYI it's my first pull/merge request so let me know if what I'm doing is correct.