BibTasklets: new tasklet

* to harvest from EDP Sciences
  FTP server.

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
I would suggest a change of logic here to avoid walking through the filesystem (which on AFS might be really slow) to find the files to convert and rather have it supplied in memory as a list.

For example:
```
xml_files = extract_files(...)
convert_files(xml_files, ...)
```
What do you think?