BUG: Fixed instability of orientation interpolation due to gimbal lock

Orientations cannot be interpolated or filtered when represented as rotations around 3 orthogonal axes (Euler angles) due to gimbal lock issue. This caused the module to be unusable for filtering transforms coming from an intertial measurement unit. Solution: replaced Euler angles representation to quaternion representation and implemented SLERP interpolation.

Also replaced obsolete GetMatrixTransformToParent() calls with new ones (that requires a vtkMatrix4x4* as input).
Merge pull request #2 from lassoan/master

BUG: Fixed instability of orientation interpolation due to gimbal lock