[Bug] Reading input paths is not relative but from offgridders main directory

[smartie2076]

When executing Offgridders with

>python Offgridders.py NESP2_NDC/inputs/input_template_excel.xlsx NESP_2_Tests/outputs_martha

Ie. for simulation inputs in a sub-folder then the error message

Traceback (most recent call last):
  File "Offgridders.py", line 275, in <module>
    main()
  File "Offgridders.py", line 69, in main
    ) = excel_template.process_excel_file(input_excel_file)
  File "D:\PycharmProjects\offgridders\src\B_read_from_files.py", line 55, in process_excel_file
    shutil.copy(path_from, path_to)
  File "C:\ProgramData\Miniconda3\envs\offgridders_python3-6\lib\shutil.py", line 245, in copy
    copyfile(src, dst, follow_symlinks=follow_symlinks)
  File "C:\ProgramData\Miniconda3\envs\offgridders_python3-6\lib\shutil.py", line 120, in copyfile
    with open(src, 'rb') as fsrc:
FileNotFoundError: [Errno 2] No such file or directory: 'D:\\PycharmProjects\\offgridders\\inputs\\timeseries\\NESP_2.csv'

Terminates the simulation.

Version: dev, 2020-07-09