Alekhine - Chess Champion

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* Added training mode based on Spaced Repetition - it combines erroneous exercises with new ones and presents the more suitable set of puzzles to solve.
* Added ability to launch tests on bookmarks.
* Added daily goal for puzzles - chose how many exercise you need to keep your skills in shape.
* Added daily streak - how many days in a row the daily goal is completed.
* Various fixes and improvements