Spline Refactor

Refactor the Spline class into two parts SplinePath and Spline.

### Spline

This is the mathematical functionality separated out that provides Bezier Curve (for now, working on Catmul Rom) Interpolation for float, Vector[2,3,4] and Color. It provides functionality for:
* Management of Knots (Control Points).
* Getting a position along the Spline from 0.0f - 1.0f.
* Management of Interpolation Mode.

Note Linear Interpolation is provided by using only two Knots or Control points in Bezier Curve Interpolation Mode.

### SplinePath

This is the Component part that provides functionality to move a specific Node along a path defined by Interpolating over a set of Control Points defined by the specified Nodes, it provides the functionality for:
* Moving the Controlled Node along the Spline based on Speed.
* Setting the Controlled Node's position along the Spline.
* Debug Rendering.
* Setting the Interpolation Mode.
* Getting a Point from the Spline from 0.0f - 1.0f.
* Management of Control Points based on Nodes.

This is a Vector3 implementation.

Debug Rendering Example
![Debug Rendering](https://dl.dropboxusercontent.com/u/30584379/Urho/splinepath-debug.png)

fixes #229