* Migrate ChainStarted and StateInitialized to state notifier
* Provide state notifier to powchain service
* Merge remote-tracking branch 'upstream/master'
* Merge remote-tracking branch 'upstream/master'
* Remove commented line
* Merge branch 'master' into master
* Merge branch 'master' into master
* Merge remote-tracking branch 'upstream/master'
* Merge branch 'master' of github.com:mcdee/prysm
* Accept err from HeadState() as non-fatal
* Merge branch 'master' into master
* Merge branch 'master' into master
* Merge branch 'master' into master