'Get a new session number.'

@needs_sqlite
def new_session(self, conn=None):

    if (conn is None):
        conn = self.db
    with conn:
        cur = conn.execute('INSERT    INTO    sessions    VALUES    (NULL,    ?,    NULL,\n                                                                                                                NULL,    "")    ', (datetime.datetime.now(),))
        self.session_number = cur.lastrowid
