[Enhancement] Add setExpandedNodes([]) to QTree

[hawkeye64]

The setExpandedNodes([]) function would take an array of node keys. The code would walk the array items and for each node that has not been lazy loaded, call the lazyLoad function and then the expansion.
This would be particulary useful where children of child nodes are known, but not yet loaded.
For instance, if using a QTree to visualize the User's HD in an Electron environment, one could call (on windows):
setExpandedNodes(['C:\Users', 'C:\Users\Hawkeye64', C:\Users\Hawkeye64\Videos])
and the final node expanded would be 'C:\Users\Hawkeye64\Videos' even if 'C:\Users\Hawkeye64' had not previously been expanded or previously lazy loaded (it would lazy load it them move to the next one).

[rstoenescu]

There's setExpanded() method (at least in v1).