CBLT-299:  copy JavaScriptCore.framework into Extras dir

Change-Id: If945b5f8a56e770726073663cb7a2364e274ec0d
Reviewed-on: http://review.couchbase.org/37760
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>