IO interfaces split / DFS

> Related PR: ezsystems/ezpublish-kernel#1017
> Status: just to run BDD tests for now

Adds `OneupFlysystemBundle` to the kernel.

## TODO
- [ ] Revert 341e3cf before merging
IMO I agree with you, plus we'd be able to use the SF kernel manipulator tool to add/remove bundles (which currently doesn't work that well if one already exists without the FQN).

Maybe a separate commit/JIRA? :)
Just my 2 cents