Consolidate JSON utilities

i seems confusing to me that we are having multiple different json utilities in the
current oak stack:

• a dependency to google-json
• a complete json utility including parser, json abstraction in oak-jcr (org.apache.jackrabbit.oak.jcr.json)
• another json utility in org.apache.jackrabbit.mk.json containing tokenizer et. al.

imo we should only have one single json utility and i would therefore suggest that
we discuss this issue and try to reach a consensus which json-library we want to use.

what do you think?