add OperationTimer
add timer methods in Observable.java
add OperationDelay
copy delay test by @jmhofer

source: https://github.com/jmhofer/RxJava/blob/e9027293dadf846b64f62e91da7c5c5850ed76f5/rxjava-core/src/main/java/rx/operators/OperationDelay.java
add delay methods in Observable.java (copied those by @jmhofer)

source: https://github.com/jmhofer/RxJava/blob/18d40522bb19f80c0ff8d4079bcb925742efecf4/rxjava-core/src/main/java/rx/Observable.java
make OperationDelayTest test Observable.delay instead of OperationDelay.delay
Merge pull request #576 from samuelgruetter/delay2

Timer and Delay