Fix crash when setting torsion angles PR#666.

Crash from incorrect memory access with SkeletonTree class.
Make sure root node is initialized to NULL to avoid deleting.
Also make sure to invalidate property table cache.
Now setting a torsion rotates the angle and properly updates data.

Change-Id: I667cd3ac21d6cb59486483e6752210d5d393722d
Merge topic 'FIX_torsion-set-crash' into master

86735b12 Fix crash when setting torsion angles PR#666.