(bug 52799) Dump JSON of entities listed in file.

This allows dumpJson.php to dump just those entities given in
a given list file.

Change-Id: Ie101cc58b0218d623e73b832a4fc9d45f1d1ac4a
(bug 52799) Filter JSON dump by shard or type.

This introduces filtering based on entity type, as well as sharding
based on ID hash.

Change-Id: I402a333f71db96b56f9c04ea2b24807abb303280