Changed the data structure of the Word POJO.

Below are some of the Words I have stored in the MongoDB Collection called words.

/* 0 */
{
    "_id" : ObjectId("536a88ce37bd12c7b24d8ef2"),
    "id" : 1,
    "word" : "APPLE",
    "hints" : [
        {
            "id" : 1,
            "hint" : "Its a fruit"
        },
        {
            "id" : 2,
            "hint" : "Its red in color"
        },
        {
            "id" : 3,
            "hint" : "Having one of this fruit everyday, keeps the doctor away"
        }
    ]
}

/* 1 */
{
    "_id" : ObjectId("536a89ae37bd12c7b24d8ef4"),
    "id" : 3,
    "word" : "COMPUTER",
    "hints" : [
        {
            "id" : 1,
            "hint" : "Its a machine"
        },
        {
            "id" : 2,
            "hint" : "It has revolutionized the way we do business"
        },
        {
            "id" : 3,
            "hint" : "Does many of the mundane tasks repeatedly and accurately"
        }
    ]
}

/* 2 */
{
    "_id" : ObjectId("536a893237bd12c7b24d8ef3"),
    "id" : 2,
    "word" : "MANGO",
    "hints" : [
        {
            "id" : 1,
            "hint" : "Its a fruit"
        },
        {
            "id" : 2,
            "hint" : "Its sometimes green or yellow in color"
        },
        {
            "id" : 3,
            "hint" : "Said to be the king of fruits"
        }
    ]
}