BibSched: email-logs-on-error parameter

* Adds a new parameter `email-logs-on-error` available to all BibTasks
  that allows you to activate an e-mail alert to task submitter
  if the task should fail (and only if it fails). E-mail alerts for
  successful tasks are still available through the `email-logs-to`
  option.

* Improves the readability of the standard e-mails sent with
  `--email-logs-on-error` or `--email-logs-to` options.
  (PR #2205)

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Merge branch 'bibtask-better-emails-on-master'

* Includes commit to complement just merged improvements
  on BibEdit.

Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>