Twaeks on pull requests # 625 and # 578

@dsaff
@kcooney
I hope you will not kill me now :)

All necessary changes regarding concurrent RunNotifier are here.
It's clear documentation for others as well.
It was hard for me not to be lost in #625 and #578, and for others could be even much harder.

I did NOT ignore the addons of both authors.

Tests:
+ AllTests
+ ConcurrentRunNotifierTest (from mine repo)
+ SynchronizedRunListenerTest (from Kevin's repo)
+ RunNotifierTest (added bottom tests from my repo)

Code:
+ RunListener (only important Javadoc)
+ SynchronizedRunListener (simple synchronization because of simplicity and modern VM optimize fast)