[Tails-dev] Improving the bug reporting workflow

I worked on fixing the issues raised by both of the recent threads
related to the bug reporting workflow:

- « Point the "Report a bug" desktop launcher to "Help & Support"? »
- « Should we avoid using the word bug? »

That's branch 'doc/improve_bug_reporting_workflow' both in the main repo
and in the whisperback repo.

Can you have a look and comment on the result? I don't pretend things
are ready to be merged, since at least I'd like to rescue some
translations. But I'd like to have your first impression on that work
before going any further.