Download error page and helper

[germa89]

Adding download section:

And also adding a helper:

def _download_file(filename, directory=None):
    url = _get_file_url(filename, directory)
    try:
        return _retrieve_file(url, filename)
    except Exception as e:  # Genering exception
        raise Exception(
            "For the reason mentioned below, retrieving the file from internet failed.\n"
            "You can download this file from:\n"
            f"{url}\n"
            "\n"
            "The reported error message is:\n"
            f"{str(e)}"
        )

Close #1156

[akaszynski]

LGTM. Thanks for adding this!

[codecov]

Codecov Report

Merging #1283 (3d2f580) into main (8493c2f) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1283      +/-   ##
==========================================
+ Coverage   75.86%   75.88%   +0.02%     
==========================================
  Files          43       43              
  Lines        6765     6768       +3     
==========================================
+ Hits         5132     5136       +4     
+ Misses       1633     1632       -1