Resolve RAP-206 "Log diagnostics"

This MR implements logging of various image diagnostics (some of which were added in RAP-209):

• theoretical thermal noise and min and mean rms noise as measured from the image (by PyBDSF) -- added in RAP-209
• Restoring beam details (minor / major axis & angle) -- added in RAP-209
• dynamic range -- added in RAP-209
• fraction of unflagged data -- added in this MR
• estimates of the astrometry and flux scale accuracy (from a comparison to the TGSS catalog) -- added in this MR

The above values are logged to work_dir/logs/rapthor.log. Some unrelated default settings were also updated.