Lock stats reports when they are submitted
Lock stats reports when they are submitted

After they are submitted, they should never be changed anyway. However, when
validate is run, it updates the valdated result and subsequently the updated_at
timestamp unless the sheet is locked.

This change will prevent any modifications after it is submitted

rlorenzo/tmlpstats,tmlpstats/tmlpstats,rlorenzo/tmlpstats,tmlpstats/tmlpstats,rlorenzo/tmlpstats,rlorenzo/tmlpstats,tmlpstats/tmlpstats,rlorenzo/tmlpstats,tmlpstats/tmlpstats