Naming: Use Segment and Sector instead of Chord and Slice

Migrated from https://bugs.launchpad.net/inkscape/+bug/774738

Summary:

Typical mathematical term for the chord is a segment (well, it's the arc + chord) http://en.wikipedia.org/wiki/Circular_segment

and

Typical mathematical term for slice is a sector http://en.wikipedia.org/wiki/Circular_sector

Note: these terms can be found in the tooltips of the ellipse/arc toolbar (also the sodipodi:arc-type but that's a bit more complex to change)

Version Info:

Inkscape 1.0 and later