Release 1.2.2

A number of fixes in this release address issues arising from the akka upgrade
in 1.2.0.

Fixes
======
7574dfc Do not send out-of-order events to StateSupervisor
d28af99 prune dead members from memberAgents
2fcd04c add periodic state check for leader state
a770ea1 Return false for timed-out `isOnline` calls
e424df9 start a scout if remote leadership fails

Default configuration changes
======
7c6e757 Gate failed connections for 200ms
391e8a2 Adjust values to line up with 2.3 defaults
b547e8c Disable quarantining, dial back health sensitivity
3880065 Lessen default LeadershipPing interval

New Features
======
834c0fa De-stringify non-string config values
3ad2289 Introduce .getDouble and .getInt to SiriusConfig
232b7cd More precise downcast for .getProp
f6e2f1f Augment MembershipActor monitoring

Documentation
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a529dfc Updated external documentation links.
8679d6e Fix external links in Scaladocs.
8a5c865 Add links for issues and questions.

Project Maintenance
======
4f43707 use bintray for dependency resolution
616900c Upgrade to sbt 0.13.2