Created Word class and Category class

build.gradle

core/src/com/wordbattle/game/model/Category.java

core/src/com/wordbattle/game/model/CreateWords.java

core/src/com/wordbattle/game/model/Word.java

core/src/com/wordbattle/game/model/WordTest.java

core/src/com/wordbattle/game/model/words.txt