Bug of get_baseline() function of Spectrum class

[BlehMaks]

🐛 Describe the bug

1. radis.spectrum.operations.get_baseline() function has a peakutils module dependency which is not included in RADIS dependencies.

2. There is a missing parameter in radis.spectrum.operations.get_baseline() function call. There also should be a wunit parameter for Spectrum.from_array() correct work.

💡 Possible solutions

1. The first can be solved by: conda install -c conda-forge peakutils, suggested by @erwanp

2. The second can be solved by adding wunit parameter to the line 1049 and 1076 of

1049: def get_baseline(s, var="radiance", wunit="nm", Iunit=None):
1076:         w1, baseline, var, wunit=wunit, unit=Iunit, name=s.get_name() + "_baseline"