Allow views to be deleted

This is an initial working implementation for view removal.

Now, the question is: Should view removal be handled separately in the UI? This implementation deletes views if the action for jobs is "Delete." This is not ideal because "Disable" does not make sense for views. At least the wording should be changed. I can continue working on this once the direction is clear.
viewName may be a relative path when using folders, like `project-a/test-jobs`. `ViewGroup.getView` will not work for paths, your need to compute the view name from the path, see `JenkinsJobManagement.createOrUpdateView`.