title: Aggregate measure as a parallel period up to parallel date
body: <p>The goal is to sum values up to the given date. So when the user chooses date range from 2021-01-01 to 2021-02-07 and aggregates it daily, the aggregation for each day is the running sum of parallel period in previous year i month aggregation.</p>
  <p>So the value for 2021-01-01 would be 2020-01-03 (monday to monday).
  The value for 2021-01-05 would be running sum of values from range 2020-01-03 to 2021-01-07.</p>
  <p>So we are trying to catch the given date and return the sum of values that fall between the start of parallel period of previous year and the date.</p>
  <p>Sample code:</p>
  <pre><code>    [date selected] 
  EXISTING [Report date].[Date YQMD].[Day]    
      
      
  sum(    
  {   
  ParallelPeriod( [Report date].[Date YQMD].[Year],   
  1,  HEAD([date selected],1).Item(0) ) 
  
  :   
  ParallelPeriod( [Report date].[Date YQMD].[Year],   
  1,  TAIL([date selected],1).Item(0) ) 
  
       }, 
          [Measures].[TTV])   
  </code></pre>
  <p>So we try to catch the date in current aggegation and sum TTV for the parallel period of previous year.</p>