R/calculate_intensity.R: minor cleaning

Signed-off-by: Charles Joly Beauparlant <Charles.Joly-Beauparlant@crchul.ulaval.ca>
R/calculate_intensity.R: merge matrix step now merge every matrix in each group

Signed-off-by: Charles Joly Beauparlant <Charles.Joly-Beauparlant@crchul.ulaval.ca>
R/calculate_intensity.R: Removed unused pvalue function

Signed-off-by: Charles Joly Beauparlant <Charles.Joly-Beauparlant@crchul.ulaval.ca>
R/calculate_intensity.R: Added the code for the bootstrap step

Signed-off-by: Charles Joly Beauparlant <Charles.Joly-Beauparlant@crchul.ulaval.ca>