Fix size hint for pqTreeWidget

The class pqTreeWidget has now a parameter MaximumRowCountBeforeScrolling.
It allows stretching the widget longer and avoid scroll bar in some cases,
which is better when there is extra space.

Change-Id: Ib8df175e7e05a0ac00573443fb8c18d4be33ed99
Merge topic 'fix_size_hint_pqTreeView' into next

f82e558b Fix size hint for pqTreeWidget