Manage remote servers infos

[relf]

This PR refactors the management of login infos.

• Now wop stores remote servers (a.k.a remotes) login infos (when successful). For instance, after a successful login sequence with wop login https://remote.example.com and API key input, further required login to this url will be simply done automatically with wop login remote.
• New command options:
  • wop list/logout -r: lists known remotes.
  • wop logout -r <name>: remove remote info specified by its name.
  • wop logout --all: remove all remotes infos.
• API change:
  • whatsopt_client.WhatsOpt(): login keyword argument is deprecated.
    WhatsOpt(login=False) should be replaced by WhatsOpt() with further wop versions.
• Breaking changes:
  • Now WhatsOpt() does not "log in" automatically:
    • WhatsOpt() or WhatsOpt(login=True) has to be replaced by WhatsOpt.login()
  • Remove PROD_URL, INTRANET_SERVER_URL constants
  • Remove default_url property

That leads to major version bump 2.0 (still in beta though... besides further testing, 2.0 may embark other features).