Plot Sun and Moon on sky temperature chart.
Plot markers on Galactic line-of-sight chart.
Create animations from Galactic line-of-sight chart.
Allow weather at antenna location to be downloaded from openweathermap.org
Allow target to be entered as Galactic longitude / latitude.
Add azimuth and elevation offsets to support scans around targets.
Add S7, S8 and S9 targets.
Refactor some code from GUI to main plugin, so computed values can be used in other plugins.
