Add vertical selection in interactive plot session

[smoia]

At the moment, the "selection" of peaks in the interactive plot session can only be done by dragging and selecting an area horizontally - which is great for some signals and purposes, but not for all (e.g. CO2 peak detection for CVR mapping).
In #20, there is already the idea of adding single-click actions to remove peaks (which would help immensely).
Another way to improve this practice would be to to drag and select a vertical section of the plot. This would again help in cases such as CO2 and CVR mapping, since peaks that might be detected erroneously but are clearly below a certain threshold could be removed manually, without having to re-run the peak detection.