Fix bug where HFR and Eccentricity were not updating in FitsViewer
This was reported on the forum https://indilib.org/forum/general/10417-hfr-not-updating-in-fits-viewer.html and then added as this issue: #132 (closed)
Probably a long-standing bug. Basically there were two code paths, one for adding an image to a new fitsviewer, and one for adding an image to an existing fitsviewer, but the status bar was only updated for the new fitsviewer.
I also added caching for the hfr and eccentricity, so it's not recomputed on switching fitsviewer tabs.