Eeschema: Implement orthogonal dragging

This is still rough and has a lot of bugs.

Here's a demo video: 2021-09-04_09-08-08.mkv

Definitely broken:

• Buses / bus entries
• Labels aren't dragged with segments unless attached to an endpoint
• Dragging test points and junctions won't add a segment
• Non-orthogonal lines explode when dragged by one end
• Junctions don't properly grab other selected items in some cases
• Duplicating lines is broken
• Selection needs to be sorted based on direction of move (do we have a function for this?)
• Selection is broken after a drag is ESC keyed out of.

Other changes, that might be 6.0 fixes:

• If you select just one end of a wire, I changed the highlighting of the unselected end to make it obvious its not selected. Commit 0a91687c
• Selected wire ends now works in multi-select mode. Commit 169ea852

I'm using this schematic as a test right now: d.kicad_sch