Force compatition agents to use latest startDate

This means they'll only have data for the current season. It might be
nice to keep the "earliest start date" as another property so we can
still have data for previous seasons. Alternatively, add "most recent
start date" and use that to provide a "this season's matches" lazy
val.
Merge branch 'competition-stages-wallchart-single-season' into competition-stages-wallchart
Merge remote-tracking branch 'origin/competition-stages-wallchart' into competition-stages-wallchart
Add wallchart ordering for WC2014

Knockout has been generalised to:
* KnockoutSpider - for knockouts with ordering info for spidering
* KnockoutList - for all other knockouts

The World Cup 2014 wallchart is the former, but KnockoutList lets us
neatly support an overview for all other tournaments (with trivial
extra code)