Implement User Qualifications 

Should be able to handle the DOSB license for "Übungsleiter", "Trainer" and "Vereinsmanager".

Draft
```
pub struct Qualification {
    pub qualification_id: u8,
    pub title: String,
    pub url: Option<String>,
    pub notes: Option<String>,
    pub valid_date: Option<chrono::NaiveDate>,
}
```