adds columns for O and D Stats to Weeks
adds oAVG and dAVG on Week List template
(style) tabs to spaces
change column type Week. oAVG dAVG to float. closes #9
adds Week#calculateStats
adds WeeksController#stats

before_action :set_week
supports week.oAVG and week.dAVG on templates
adds js response for WeeksController#stats
adds route for 'stats'

stats_week_path(@week)