a) add a new optional poincare plot parameter named
-group_data_filename  (--group_data_filename)
used as a file where are stored all input files according to data_dir
and extension 
and this overall file is used as a input file for further analysis;
changes in:
package hra_math.time_domain.poincare_plot.poincare_plot,
class hra_math.model.parameters.file_data_parameters.FileDataParameters

b) add in package hra_core.io_utils a new function:

def join_files(_filenames, outfilename, first_headers_only=True,
headers_count=0)

which joins many text files into one file