[server] Introduce an `has_scheduler` method on Repository This is to be used by client application to determine if looping tasks may be registered in the current process. By checking this, one will avoid the warning in looping_task method when the repository has no scheduler.

[bdist_wheel]
universal = 1

[check-manifest]
ignore =
  debian
  debian/*
  cubicweb.spec
  __pkginfo__.py