Rewardify

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* Extended the clean method for the Environment setup of the test cases to also remove sub folders

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* Added "user.save()" calls to all the methods of the facade, that modify the models, so that the modifications
actually get taken over into the database

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* Fixed, that the facade method for buying a pack internally called the method for adding a pack, thus not
actually spending gold on it

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* Internal changes in the recycle method for rewards
* Added a "user_exists" method to the facade, which will return, whether or not the given user
name exists in the database or not
* Added "effect" field to Reward class
* An optional string item "effect" can ba added to the config of any reward. This string should contain
special syntax, for what effect the reward usage should have on the rewardify system
* Currently granting the user gold and dust are supported effects
* Added more methods for handling rewards to the facade, which include buying, using and recycling
rewards

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* Fixed bug in setup.py, which caused the "backends" package to be excluded

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* Initial version