Add the ability to collapse and expand SplitPanel

[Flaurite]

Description

Now if it is necessary to expand or collapse SplitPanel we have to use setSplitPosition().
This method will save the given position as last, so when we click on the dock button it won't be moved.

It would be helpful if it has methods to expand or collapse SplitPanel and do not change the last known position.

See forum: link