fix the issue of Property priority not respected in sticky event

[tomridder]

fix the issue of Property "priority" not respected in sticky event #656
reason of issue:the list subscriberMethods is not sorted by priority before postSticky
solution: sort the subscriberMethods by priority
ps:i add the testcase in EventBusStickyEventTest and it passed ... and all test case in EventBusTestJava and EventbusTest module are all passed
:)

[greenrobot-team]

Thanks! We'll consider this in an upcoming release.