spectral vs. average Tsys

[teuben]

the current pipeline has hardcoded (and plots) the spectral tsys, and although there is a boolean flag to switch to a constant Tsys, this would create boring constant Tsys oplots. So apart from making constant Tsys the default, the Tsys plots should keep the spectral Tsys so it's visually clear what the is that will be used by the pipeline.