Add category; Change equals methods in Game, Puzzle, and User; Add getAllCategories in Db service
Merge branch 'category-support' of https://github.com/Tokanagrammar/tokanagrammar-dev into category-support
introduce the category class
Merge pull request #95 from Tokanagrammar/category-support

Add category; Change equals methods in Game, Puzzle, and User; Add getAl...