Neue Route für Hauptansicht

• Add new Route GET /questions/overview that includes number of new replies and category info (see below), deprecating GET /questions/categories
• Move activity timeframe (24 h) to constant

{
    "newReplies": 1,
    "categories": [
        {
            "id": 1,
            "title": "Help",
            "description": "Hilfe bei allgemeinen Fragen",
            "logo": "",
            "countActivities": 0,
            "subcategories": [
                {
                    "id": 7,
                    "title": "Wo ist was?",
                    "description": "Fragen zu Locations etc.",
                    "logo": "",
                    "countActivities": 0,
                    "subscribed": false
                }
            ],
            "subscribed": true
        },
        { ... }
    ]
}

Close #97 (closed)