Merge pull request #1568 from ngokevin/iarcsuccess

fix devhub ratings success msg for public apps (bug 950948)
mexico to use esrb (bug 931947)
Merge pull request #1524 from ngokevin/commando1

auto-mark old msgs as read when join thread, refactor comm tests (bug 931223)
comm api create thread (bug 946459)