specframe units

In order to approximate real spectrometer conditions, the units in the spectrometer frame should (optionally) be different:

• B0 field in 1H frequency
• Gain in decibel
• (offset in ppm?)

All of these are in the magpie.py file I believe.

For now it will sufficient to incorporate these with a simple flag that can be changed within the code. In the future this should be a setting that can be changed in the GUI.