Some differences are due to difference between libraries being files
in symbol editor and directories in footprint editor, but this unifies
most of the rest.
It also dispenses with the save-to-library vs save-to-document distinction
in the GUI because it makes for too much variability in the GUI, was
implemented differently between the two editors, and isn't needed as much
anymore now that we have the highly visible infobar.
There was also an issue that the save-to-board icon occupies the same
location and has the same size/shape/colours as the Board Setup icon in
PCBNew.
Fixes https://gitlab.com/kicad/code/kicad/issues/7215
Jeff Young
Wayne Stambaugh