Investigate moving the New Game dialog to a wizard

[alopezlago]

The New Game dialog is getting too tall. We should look into moving to a wizard, which would be broken down into these steps:

• Import the roster
• Load the packet
• Select the game format

The second and third parts could be combined together. We could also add some UI to manage custom game formats so people can download a game format once and continue using it for future games instead of having to set it through the Change Format dialog each time.