Switch from openExternal() to auth.openUri()

[happybeing]

As this is a coding example I think it is worth updating it so as not to confuse people who find the following temporary fixes. I understand from @joshuef that the Mac OSX issue has been fixed so the following code can be updated.

https://github.com/maidsafe/safe-web-hosting-manager-electron/blob/master/app/safenet_comm/network.js#L36-L38

https://github.com/maidsafe/safe-web-hosting-manager-electron/blob/master/app/safenet_comm/network.js#L52-L54