Add utility functions and ability to dynamically set host

I have added a parameter to the constructor in order to initialize the Connection with the appropriate  NetSuite domain. 
 - First I do not like the solution I have come up with.
 - Second the first parameter is a wsdl url however $nshost is used in creating the wsdl and the location header and that needs the correct domain as well.

I have also added a public and one private function to calculate the authentication token for SSO use.