SCORSRVR-17. Fix the scoring servlet to use the JSONEntityIdParser.

KijiREST introduced a better way to specify EntityIds on the URL and since the
ScoringServer has a similar problem, this mechanism was moved into KijiSchema
and now the ScoringServer can use this. Instead of specifying a string encoded
JSON array (with weird quoting due to double quoting the string and single
encoding string components), now the user (or caller) can specify a more natural
JSON array on the URL making it easier to debug issues eliminating the various
quoting problems.

Review: https://review.kiji.org/r/1745/
Reviewer: shashir, ajprax