title: Get total step count for every date in HealthKit
body: <p>What's the best way to get a total step count for every day recorded in <code>HealthKit</code>.
  With HKSampleQuery's method initWithSampleType (see below) I can set a start and end date for the query using <code>NSPredicate</code>, but the method returns an array with many HKQuantitySamples per day. </p>
  
  <pre><code>- (instancetype)initWithSampleType:(HKSampleType *)sampleType
                       predicate:(NSPredicate *)predicate
                           limit:(NSUInteger)limit
                 sortDescriptors:(NSArray *)sortDescriptors
                  resultsHandler:(void (^)(HKSampleQuery *query,
                                           NSArray *results,
                                           NSError *error))resultsHandler
  </code></pre>
  
  <p>I guess I can query all recorded step counts and go through the array and calculate the total step count for each day, but I'm hoping for an easier solution as there will be thousands of HKSampleQuery objects. Is there a way to have initWithSampleType return a total step count per day?</p>