Improved the accuracy of our graph panel when showing coordinates and zooming a region. Indeed, before, there could be cases where moving the mouse by one pixel wouldn't move the crossing lines for showing the coordinates (however, the label for the coordinates would still get updated, as expected). This was due to rounding issues following some mapping/unmapping.

Otherwise, also addressed a small issue related to the fact that we now use QRect rather than QRectF in some cases, and that for historical reasons some of its methods (e.g. bottom(), right() and bottomRight()) don't behave the same way as its QRectF counterparts.