SLING-3693 - Repository import wizard blocks UI thread and is not
cancellable

Use ProgressUtils in the wizard classes.

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1605087 13f79535-47bb-0310-9956-ffa450edef68
SLING-3693 - Repository import wizard blocks UI thread and is not
cancellable

Tweak the import wizard

- better import feedback ( although we still don't estimate total work )
- operation can be cancelled in a reasonable amount of time
- minor internal cleanups in ImportRepositoryContentAction

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1605088 13f79535-47bb-0310-9956-ffa450edef68