When switching columns layout to less columns, widgets should be moved to visible column

[mattab]

Bug: When moving from a 3 columns dashboard to a 2 columns dashboard, the widgets in the third columns are hidden and lost.

Expected: The widgets from any column hidden after changing layout, should be moved to the visible columns. Ideally widgets will be "distributed" among columns. Eg. if 4 columns layout becomes 3 columns, if the hidden column had 4 widgets, column with the least amount of widgets would have 2 extras, and the 2 other columns would have 1 new widget each.

Ie. Each column could get a new widget in turn, starting with the one with the least widget.

[sgiehl]

(In [7769]) fixes #3674 move widgets to remaining columns if column count is reduced when switching dashboard layout. Widgets are moved based on the height of the remaining columns. each widget is moved to the column with the smallest height (which changes while moving widgets)

[mattab]

Very nice fix!!