Gamification Engine:

- service implementation:
	- improved and refactored the getCustomizedGamificationPluginsList service (3 services in one for all types of customized gamification plugins)
	- improved and refactored the related tests
	- improving and refactoring of the other services (by adding new input/output elements) and of the models (adding or improving keys)
	- introduced the concept of CustomizedGamificationPlugin