In particular, don't move block back to start when duplicating,
and don't move crosshair back to start when doing a cut, copy, or
paste.
Also fixes undo for libEdit block duplicate.
Fixes: lp:1740138
* https://bugs.launchpad.net/kicad/+bug/1740138
1) when duplicating don’t keep original hidden until end of drag
2) reset selectionArea when showing it so it doesn’t flash in its previous location
3) center a pasted block on the cursor
4) don’t draw the source selectionArea when pasting a block
5) implement selection-style highlighting for contents of blocks
6) add pasted items to view so they don’t disappear when the block is placed
Fixes: lp:1747197
* https://bugs.launchpad.net/kicad/+bug/1747197