Toward merge tool #50

With the branch https://github.com/OpenGATE/GateTools/tree/mergeTool , I want to create a tool to merge Gate jobs together. The jobs were previously create using cluster https://github.com/OpenGATE/GateTools/blob/mergeTool/clustertools/gate_split_and_run.py .
First I want to list all Gate output files in order to be merged:

• .hdr image containing "INTERFILE" word (https://gitlab.in2p3.fr/tbaudier/simu-psf/)
• .hdr image (missing example)
• .mhd/.mha image containing "Uncertainty" word (https://github.com/OpenGATE/GateContrib/tree/master/dosimetry/Radiotherapy/example1)
• .mhd/.mha image (gt_image_arithm)
• .root
  • Tree
    • example of PET (https://github.com/OpenGATE/GateBenchmarks/tree/master/t5) (gt_merge_root)
    • example of phase space (https://gitlab.in2p3.fr/davidsarrut/gate-exercices/-/tree/master/linac) (gt_merge_root)
  • T1D (example https://github.com/OpenGATE/GateBenchmarks/tree/t3_range_e+) (gt_merge_root)
• .txt file containing "NumberOfEvent" word (stat file)
• .txt file containing "energydose" word (dose file) (missing example)
• .txt file containing "Resol" word (text image) (missing example)
• .txt file containing "vol(mm3)" word (https://github.com/OpenGATE/GateContrib/tree/master/dosimetry/doseByRegions)
• .txt file (concat) (missing example)