Add field for pair go partner on registration form

[vash3g]

Is your feature request related to a problem?

Registration form has field to enter server name for pair go.

Describe the feature you'd like to see on the Go Congress Website.

Add field for Partner Pandanet username to match people together. We can match people up for pairings post closed registration/before event.

Notes

Add any other information or screenshots about the feature request here.