Ensure hraven-client does not require hbase dependency at run time

[vrushalivc]

the hRaven client should not depend on any hbase jars at run time. This is important so that clients can make REST calls and expect java objects being returned.

I believe this class needs to be looked at in more detail, specifically line 63

return om.readValue(inputStream, type);

https://github.com/twitter/hraven/blob/master/hraven-core/src/main/java/com/twitter/hraven/util/JSONUtil.java