Add 25 and 75 percentile of TRX times for TPROC-C

[hgxl64]

HammerDB currently reports the minimum, median, avg, 95 and 99 percentile and maximum execution times of the 5 TPROC-C transactions. In order to draw a standardized box-and-whisker plot we also need the 25 and 75 percentile (aka 1st and 3rd quartile) of the execution times.

The XT profiler seems to be able to get any percentile we want. So please add the code to extract the 25 and 75 percentile and write them to hdbxtprofile.log.

Box-and-whisker plot: https://en.wikipedia.org/wiki/Box_plot

[sm-shaw]

Issue #765 references memory issues with the current response time capture as the data for each transaction is recorded. Moving to a sampling based approach appears to be the most straightforward solution and therefore the goal will be to implement that with the fix for this issue. We will also look into producing the box-and-whisker plot in the webservice alongside the current bar chart.