Eeschema:
* Graphic texts ans labels: fix fully broken undo/redo code relative to the way undo/redo command
* handles changes (maintly move) for labels
* Fix minor bug for undo command relative to block rotate
* Remove dead code.
* Add new class BITMAP_BASE, and (for Eeschema) SCH_BITMAP to handle bitmap images in schematic.
Remember plot Bitmaps in not possble with all plotters.