BibTasklets: new bibtasklet to send a post request

* with the record ids that webcoll has processed.

If the site is down, this will spin forever. Perhaps there can be a fixed number of retries before exiting with error. For BibSched to detect error you can: (a) raise some exception, (b) return non-zero value, like 1 or (c) use `bibtask.task_set_status` to set it to "ERROR" or something like that.

Note that requests can do the retrying for you: http://docs.python-requests.org/en/latest/api/?highlight=max_retries#requests.adapters.HTTPAdapter