Update for RxJava 0.17.0-RC1

This is the release candidate version, which is being currently tested
at Netflix. In a few days, I'll update with the final version.

This release cleans up some bits of RxJava by integrating the
subscription inside a subscriber (which is an observer holding a
subscription) and fixes a leak with recurring tasks.
refactoring: use RxJava to download preview map
Intercept InterruptedException in chained observables

The source of those exceptions need to be investigated further.
Proper use of schedulers with RxJava downloading
Make explicit use of Schedulers and document it
Fixes #3617, Archived message is shown as note

- added this, and some other missing log types, to OkapiClient