use opendata.dwd.de to read radolan and dx data

[kmuehlbauer]

direct access of opendata.dwd.de:

from ftplib import FTP

def open_ftp():
    host = "opendata.dwd.de"
    user = "anonymous"
    password = "anonymous"
    ftp = FTP(host)
    ftp.login(user, password)
    return ftp

def get_dirs_ftp(ftp, folder=""):
    contents = ftp.nlst(folder)
    folders = []
    for item in contents:
        if "." not in item:
            folders.append(item)
    return folders

ftp = utils.open_ftp()
ftp_dirs = utils.get_dirs_ftp(ftp, "weather/radar/composit/rx/")
filelist = ['ftp://opendata.dwd.de/' + item for item in ftp_dirs]
data, meta = self.rfunc(urlopen(self.filelist[0]))