Implement SpectralGaussian model class #2244
@JouvinLea - Thanks!
There's a conflict in
@registerrier - Could you please review this PR and merge it in when ready?
I don't know, I recalculate evrything my self. I think for the integral it is ok since the result is quite obvious and in the test I add a check that the integral between -inf and inf is q=equal to the norm No.
For the energy flux, it is true that the test is not a super good test since I didn't what to test to know If analytical integration was correct.