Allow gzipped CSV input files

[tucotuco]

Allow gzipped CSV input file uploads and processing, including reading the header out of them.

[tucotuco]

See if seek can be done inside a zip file to find header in api.py and if so, allow zip file uploads.
Try something like
$ gzcat Downloads/2fieldsblank-eb899df3-5e6f-4e17-9606-3101f8b26aba.csv.gz | head -n 1
from https://unix.stackexchange.com/questions/452011/read-first-line-from-gz-compressed-file-without-decompressing-entire-file