Remember what the user entered on the login page

Record the user's login info so it can be shown as the default the next time the user logs in. 
Would consider storing the password? My reasons:
1. I'd prefer not to enter my password whenever I start the client. 
2. IRC is an insecure protocol, so I suspect users would realize that they shouldn't use a sensitive password to protect their nick. 
3. Users have requested a similar feature in issue #611. 
4. Other clients provide this functionality. 

I'll use the global setting object to record the previous values.