Optimize Store#where and #parseObjects.
Optimize Store#where and #parseObjects.

Array#concat, while more efficient for joining two arrays, allocates
a new array on each call and thus is inefficient when done in iteration
over large numbers of objects. Instead, we can use Array#push, as we
don't mind mutating our accumulator. This quick benchmark script
demonstrates the improvement:

  var items = _.fill(Array(10000), 1)

  console.time("concat");
  _.reduce(items, function(res, i) { return res.concat(i); }, []);
  console.timeEnd("concat");

  console.time("push");
  var arr = [];
  _.forEach(items, function(i) { arr.push(i); }, []);
  console.timeEnd("push");

 concat: 895.499ms
 push: 1.484ms

dscout/immunid,dscout/immunid