Make Crucible settings application wide

* Let CrucibleManager be a project service.
  It seems that it was intended to be a project singleton,
  but appeared to be an application singleton with myProject
  remembered forever.

* Make CrucibleConfigurable be an applicationConfigurable, and
  CrucibleSettings be an application service, and store it in the
  APP_CONFIG folder.
  Since the CrucibleTestConnectionTask requires a project, give it the
  default project. Actually, the project is needed only for the
  CrucibleSessionImpl, and not for the logic request,
  but it can be fixed later.

* CrucibleSessionImpl: don't calculate roots in the constructor,
  do it on demand (otherwise calculating roots for default project
  leads to an error, and it is not needed here anyway).