addNewUsageStat method
Implementation
void addNewUsageStat(String key, DateTime whenStarted, Duration usedFor)
{
List listOfUsage = this.analytics[key]['usedWhen_howLong'];
Map newUsageStat = {'started':whenStarted, 'usedFor': usedFor.inSeconds};
listOfUsage.add(newUsageStat);
this.analytics[key]['usedWhen_howLong'] = listOfUsage;
}