Add leg and stage to all match types

This data comes back in every call now - it seems like that wasn't the
case in the past when the models were originally written. Adding this
information everyhwere is essential for things like the world cup
groups and knockout stages.
Round is always provided so change Option[Round] -> Round

This matches the stage and leg properties which are now always
provided as well and will simplify client code.
Merge pull request #31 from guardian/add-stage-and-leg-to-all-match-types

Add stage and leg to all match types