writing CategoryManager to JSON

src/main/java/mi/hdm/filesystem/FileManager.java

src/main/java/mi/hdm/recipes/CategoryManager.java

src/main/java/mi/hdm/recipes/RecipeSearch.java

.../java/mi/hdm/typeAdapters/CategoryManagerTypeAdapter.java

src/main/java/mi/hdm/typeAdapters/CategoryTypeAdapter.java

src/test/java/mi/hdm/filesystem/JsonTest.java

src/test/java/mi/hdm/recipes/RecipeTest.java