Better support for "The Paris Method" for board seeding

[UEWBot]

For a top board in particular, the whole power-assignment process is interesting.

Ideally, we'd be able to create a GamePlayer without a Great Power and then assign the GreatPower later.
We'd want to be able to display the power selection order and also which powers were chosen by who.
These should be added to Game.news() [e.g. "John Smith chose 3rd and picked Austria", "John Smith chose to pick a country after Joe Bloggs"].

[TimothyJones]

Arbitrary news updates could solve this without needing to model many different power selection methods.

Create the game with the players, then submit a number of news updates, then assign the powers.

This would have the disadvantage that you wouldn't have the data available in a nice format for analysis, but this selection method is rare enough that anyone who wanted to do that could just look at all the games manually.

[UEWBot]

Yeah, a way to manually inject news items would be a good feature to have anyway. There are certainly things that happen in games that are interesting but hard to identify automatically.

[UEWBot]

Currently, the power attribute of GamePlayer is mandatory, so there's no way to assign a player to a game as an unspecified power.

[UEWBot]

Commit 6dec448 makes GamePlayer.Power optional.

[UEWBot]

To have full support for top board seeding, I think we'd want a new class to track the power assignment order. It would have a foreign key for the GamePlayer, an integer for the order in which they choose their position (this would be the inverse of the position at the start of the round, but it makes sense to record it rather than figuring it out whenever we need it), and an integer for the position chosen. The actual GreatPower would still be tracked by the GamePlayer.
Once we have the class, we'd then need form(s) to enter the data and views to display it.
Finally, we'd want a way to record that the top board for the Tournament is being seeded in this way (we probably need to add a couple more attributes to Tournament - one to indicate whether the Tournament has a top board and another for the seeding method for the top board.