Add player background from series

[UEWBot]

Now that we can identify series of tournaments, it would be nice to have series-specific background for players. For example "X won this tournament 3 years ago" or "Y has finished as high as 3rd at this tournament".

[UEWBot]

This would be an addition to Player._tourney_rankings(), with a new MASK value or values to include background from the series.

[UEWBot]

Possible background items:

• Best finish in series
• Number of times player has won a series event (note that this will be an "at least" number because most series pre-date the SW)
• Previous wins in the series
• Defending champion
• Previous best result in the series as a specific power
• Previous best country awards in the series as a specific power

[UEWBot]

This isn't quite as straight-forward as I'd hoped, because Player._tourney_rankings() looks at PlayerTournamentRankings but to do this we need to go through Series. The first patch does that independent of _tourney_rankings(). Probably need to break that out into a separate method somewhere and expand it to add the other background items noted above.