Added zero to the default deck and then updated class-level comments
Added copyright comment to top of all deck related code
Update comments in deckListModel
Adds comments to all deck related classes
fix error that allows no specified date to go through as a valid change
Adds a javadoc comment to the method added to fix the validation error
Merge pull request #39 from TheTeam8s/feature-addZeroToDefaultDeck

Feature add zero to default deck
Merge pull request #40 from TheTeam8s/feature-fixDateValidationError

Feature fix date validation error
Add estimate class and list of estimates to planning poker session