Phasing: Add second order phasing

Created by: FlorianSchreiner1

There currently is no software available to interactively correct spectra with a 2nd order phase. I implemented this functionality and made it optional to display, since it is a niche application and could potentially distract new users.

The addition of this feature is important for anyone utilizing frequency swept pulses, namely WURST pulses, because these impose a 2nd order phase on the signal. This is normally dealt with by magnitude processing the spectra, at the expense of a loss of S/N. Being able to correctly phase these spectra interactively should be a nice addition to the general workflow.