BoxOfQuestions library

• Added a simple learning session implementation. When a learning session starts words are added to the wordsToRepeat collection if there are not enough words. This is determined by a new setting suggestedNumberOfWordsInASession which has a default value of 20.
• New method addMoreWordsForLearning() : it is used to move words with step < 0 to step =0 which means that the words are part of the collection wordsToRepeat. This method is called by wordsToRepeat at a start of a session.
• Added synonyms for
  • moveQuestionForward -> answerWasCorrect
  • moveQuestionBackwards -> answerWasWrong
• For test purposes the default setting for the delay value after which a question might be asked again has been set to one tenth of a day