Add 'active' property to HTTP Get Bucket Type Props API call [JIRA: RIAK-2106]

[dmitrizagidulin]

Getting bucket type props via the command line (riak-admin bucket-type status <type>) includes the active property (whether or not the bucket type has been activated).

However, doing an HTTP GET to /types/<type>/props does not include the active property.

This happens because the bucket type props jsonify code uses the same code for bucket props as for bucket type props. Except that buckets don't have the 'active' attribute.

So, need to add a function to jsonify that attribute.

(Issue #1171 is somewhat related, since you can't fetch http /props for inactive buckets at all).