Signal versus `x` plot

[trappitsch]

Create a functionality to easily plot the signal (peak integrals) of multiple opened crd files (in the processor) and plot them against a user-given value.
The idea behind this is to add a window that allows the user to plot saturation curves / wavelength scans, etc. in a nice figure without having to copy the data to excel.

In the end, the user should be able to:

• Save the curve data (wavelength/power vs. signal for individual peaks) as a csv file
• Save the figure as a pdf or similar

Low priority