Adding GameRequirementModel class

Adding a simplified requirement class for planning poker games that contains the estimates for the requirement. Moving getMedian and getMean to new class.

Authors: lhunker, dbtrue
Merge branch 'team9dev' into viewEstimates
Changing GameModel to work with GameRequirementModel

Authors: lhunker, dbtrue
Merge pull request #22 from dbeckwith/viewEstimates

View estimates
Merge branch 'team9dev' into feature-emailnotification