`class SlideViewer`: segfault depending on the image size and mouse events

[baugetfa]

The following remarks come from the use of the demo node display which displays an image using slide_viewer class:

• got Process finished with exit code 139 (interrupted by signal 11: SIGSEGV) if the image size is too big. Reproducible, for example with the following image if we reduce the size by 50% it passes, by 75% it does not
  .
• the image is displayed in the wrong direction like mirror reflection.
• the "mouse_press" is not well managed, see for instance def mousePressEvent (self, event) : in class ScalableLabel

[baugetfa]

We have the same point 3 for point_selection.

• the "mouse_press" is not well managed