Added generic spline implementation for use with camera animations.

The splines are implemented as template classes all based on an abstract spline template. The template argument specifies the type that is interpolated along the spline. Currently supported are integer and floating point types, aswell as QVector2D and QVector3D.

The splines are used for smooth camera animations, though only for the cameras location. There are currently 3 spline types implemented, a cubic hermite spline and two specializations of that, the catmull-rom and cardinal spline.

Closes #308 (closed)