Make panel scrollable when overflowing

Niccolò Venerandirequested to merge
work/niccolove/488142 into master

When there are more widgets and available space on the panel, the panel will become scrollable!

This also fixes the minimum size of the task manager so that icons can always preserve their full size.

BUG: 457536 BUG: 447603 BUG: 488142 FIXED-IN: 6.5.0

Edited by Nate Graham

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