Added Domain Class Category

Category.groovy
Added Domain Class User

User.groovy
Created Catgeory Controller and Dyanmic Scaffold

static scaffold = Category
Created User Controller and Dynamic Scaffold

static scaffold = User
Added Relationships with the Todo, Category and User

Domains:

Todo:

User owner
Category category

static belongsTo = [User, Category]

Category:

User user

static belongsTo = User
static hasMany = [todos: Todo]

User:

static hasMany = [todos: Todo, categories: Category]
Added Domain Class Task

Task.groovy