title: Set annotation X1 and X2 on BoxAnnotationViewModel to be between major grid units on CategoryDateTimeAxis
body: <p>I am using scicharts BoxAnnotationViewModel to highlight a particular selection of price data from a FastCandleStickRenderableSeries. Currently setting the BoxAnnotaions X1/X2 has undesirable results as it will place this in the middle of the desired candle as the X1/X2 input only accepts an integer index  for a CategoryDateTimeAxis. I would like to be able to offset this X1/X2 input by 0.5 units to encompass the entire candle/candle range desired. </p>
  
  <p>Is this a possibility that I have missed in the SciChart docs using the default built in BoxAnnotationViewModel on a CategoryDateTimeAxis for financial data? </p>
  
  <p>Thank you, </p>
  
  <p>Using SciChart Version: WPF 6.1.1.13136</p>