Simplify signatures of retryWhen/repeatWhen as discussed in #24

- If RxJava is updated with the same signature changes with ReactiveX/RxJava#1720, the conversion from RxScala to RxJava can be simplified, without any external signature changes in RxScala.
Merge branch '0.x' into retryrepeatwhen-updatesignatures
Upgrade to RxJava 1.0.0-RC5

- Update retryWhen/repeatWhen RxJava signature conversion to match

- Remove groupByUntil methods since they were removed from RxJava
Merge pull request #27 from jbripley/retryrepeatwhen-updatesignatures

Upgrade to RxJava 1.0.0-RC5