automatic color update through appearance- and preferences changes

support dark mode

Allow for anchor selection

read prefs for text color & size

fixes #5

Reinstate angle display

(by making the text box taller)

Rewrite using Subscriber

This work was all done by Frederik Berlaen.
Thank you, Frederik!

Fixes to observers by Frederik

Unify quotes, fix typo,

give stronger name to observer removal operation

Fix bug in BCP handle swapping.

Minor code improvements.

New images for README file.