Configuration webservice

Adding configuration webservice, will be available at .../api/config
The configuration gathers together the server tags and some preferences (max number of tags and max number of gifts).

Configuration example :
{
    "tags": [
        {
            "label": "tag1"
        },
        {
            "label": "tag3"
        },
        {
            "label": "tag2"
        }
    ],
    "preferences": {
        "numberOfTags": 10,
        "numberOfGifts": 10
    }
}