Clean-up of fitting unit test

[peterfpeterson]

There is still a fair amount of cleaning up that would make this easier to follow/modify:

1. Create a method for verifying Gaussian parameters, verify_gaussian(FitResult, height, center, sigma) which would use np.testing.assert_allclose to check the raw peak parameters.
2. Create a method for verifying pseudo-Voigt parameters, verify_pseudovoigt(FitResult, intensity, center, fwhm, mixing) to check the raw parameters
3. The checks for native vs effective parameters as that is already covered by more complete tests in test_peak_collection that are part of this.
4. The checks for cost can also dropped

This is a follow-on to #260, but should not be started until #292 is merged in.