enhance: Reduce Repeated Code

[bennjii]

Due to the early-adoption of 0.4 and 0.5 beta features in rocket, middlewares were not explored in depth (FromRequest, ..). These are now included, as well as an improvement to the Database middleware, adding a Session middleware and re-forming the return types to be more uniform and generic. Thus greatly reducing the complexity of each rocket function from an average of 8 lines to 2.

Further work is being done to reduce this to 1 line through the use of procedure macros to inline the use of validations.

The example from the Kiosk set is shown below.

// NEW
pub async fn get(db: InternalDb, id: &str, session: Session) -> Convert<Kiosk> {
    check_permissions!(session.clone(), Action::FetchKiosk);
    Kiosk::fetch_by_id(id, session, &db.0).await.into()
}

// OLD
pub async fn get(
    conn: Connection<Db>,
    id: &str,
    cookies: &CookieJar<'_>,
) -> Result<Json<Kiosk>, Error> {
    let db = conn.into_inner();

    let session = cookie_status_wrapper(&db, cookies).await?;
    check_permissions!(session.clone(), Action::FetchEmployee);

    match Kiosk::fetch_by_id(id, session, &db).await {
        Ok(employee) => Ok(Json(employee)),
        Err(err) => Err(ErrorResponse::db_err(err)),
    }
}