* Also fix scaled down pixmap when updating pixmap in the same group
* Fix ignoring mouse wheel event when max scale has been reached
* Fix toggle scrollbars when asking for normal size
* Work around flickering of scrollbars due to
GridLayout resizing on odd pixels by disabling
the scrollbars while BestFit is active
* Also setting minimum column width to work around
the issue above.
* Avoid updating scrollbar values twice by using a
simple boolean lock
Using a QWidget inside the QScrollArea mostly works
but we only move around the pixmap inside the QWidget,
not the QWidget itself, which doesn't update scrollbars.
Need a better implementation.
The controller singleton acts as a proxy to relay
signals from each widget to the other
It should help encapsulating things better if we need to
use a different class for image viewers in the future.
