Also adds Border checkboxes and fixes a bunch of bugs.
Also fixes some plot bugs with arcs. Also moves polygonization of arcs (when required) in plotting code from 5 degrees to calculated based on ARC_HIGH_DEF. Fixes https://gitlab.com/kicad/code/kicad/issues/5017
ADDED: a new label type for netclass flags. ADDED: the ability to define fields on labels.