Added documentation and game description

.gitlab-ci.yml

CCity.Model/Citizen.cs

CCity.Model/CitizenManager.cs

CCity.Model/ErrorEventArgs.cs

CCity.Model/Field.cs

CCity.Model/FieldEventArgs.cs

CCity.Model/FieldManager.cs

CCity.Model/Filler.cs

CCity.Model/Fire.cs

CCity.Model/FireDepartment.cs

CCity.Model/FireManager.cs

CCity.Model/FireTruck.cs

CCity.Model/Forest.cs

CCity.Model/GameErrorException.cs

CCity.Model/IMultifield.cs

CCity.Model/ITransaction.cs

CCity.Model/IUpgradeable.cs

CCity.Model/MainModel.cs

CCity.Model/Placeable.cs

CCity.Model/PlaceableTransaction.cs