relax SVN archive

Added new backend function in pipe_control.spectrum.sn_ratio_selection.

This is to select spins with a signal to noise ratio, higher or lower than the specified ratio.

Added the new user function deselect.sn_ratio, to deselect spins according to their Signal to Noise ratio.

Added function in pipe_control.spectrum.sn_ratio_deselection(), a function to deselect spins according to the Signal to Noise ration.

The function is flexible, since it possible to use different comparison operators.
And the function can be switched, so a selection is made instead.

Added two new systemtest in Spectrum. test_deselect_sn_ratio_all and test_deselect_sn_ratio_any.

These test the user function deselect.sn_ratio, to deselect spins with a signal to noise ratio lower than the specified ratio.

Made the user function spectrum.sn_ratio smaller.

Added float around values in signal_noise_ratio() function.

For the specific analysis of "noe", "relax_disp", and "relax_fit", initialised the sn_ratio parameter structure.

Added the common API Parameter structure 'sn_ratio' in parameter_object.

Added systemtest Spectrum.test_grace_sn_ratio to help implement plotting the signaÃl to noise ratio per residue.

Added systemtest Spectrum.test_grace_int, to test plotting the intensity per residue.

This is to prepare for a grace plotting of the signaÃl to noise level per residue.

Also added additional tests for signal to noise ratio calculation in the systemtest Spectrum.test_signal_noise_ratio.