move set_current_league in application controller

to always call it when the current_league is called. This sets the
session variable when the slug is read from params[:league_id]
Merge branch 'master' into session_league_slug
change variable name for more clarity
update specs to match change with league_slug behavior
Merge pull request #90 from stephanpavlovic/session_league_slug

set_current_league fix