joinedGroup = async (user, group) => {
  let is = await db.query(
    'SELECT COUNT(grp_member_id) AS joined FROM group_members WHERE member=? AND group_id=? LIMIT 1',
    [user, group]
  )
  return db.tf(is[0].joined)
}
Returns whether user joined group
@param {Number} user UserID
@param {Number} group GroupID