This reverts the revert commit 01c431b4466b0ac32c6c8bdf70aed078d8ec12b4.

Busy cursor is shown while expansion of the tree.

Introduced new expand methods that allow disabling redraw while
expanding the tree. The busy indicator will be shown until the tree has
been redrawn.

Change-Id: I70f815e9ca6821ae81c5e3426f865f46c7de9ce7
Signed-off-by: Karsten Thoms <karsten.thoms@itemis.de>