FormatJson::stripComments

Add stripComments method that can be used to remove single line and
multiline comments from an otherwise valid JSON string. Inspired by the
comment removal code in redisJobRunnerService and discussions on irc
about the Extension registration RFC.

Change-Id: Ie743957bfbb7b1fca8cb78ad48c1efd953362fde
Merge "FormatJson::stripComments"