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.