Add getHyperNewsName function in client_utilities. 

This is to address #4225. The getHyperNewsName function is what we already had in the checkHNname command. So now I use the function in checkHNname. 
The issue also requires to create a proxy before loading config, which I do via a new function in CredentialInteractions. I now initialize a CredentialInteractions object (self.proxy) in the SubCommand constructor, and use it elsewhere.