Allow editing of pairings

[ianpaschal]

User Story

As a tournament organizer, I want to be able to edit pairings I have already generated. I also want to be able to create them after registration closes, but before a tournament starts.

Functional Requirements

• The 'Configure Round n' tournament action is available if registrations are closed, and currentRound is undefined.
• The pairings page can also load existing pairings into the form to be edited.
• The 'Reset' button reverts to generated pairings (and 'Auto' tables), not to the last saved version.