Adding custom bezier easing curves to QEasingCurve

Adding custom bezier easing curves to QEasingCurve

I added the possibilty to define Bezier/TCB splines and use them
as custom easing curves.

Note:
Splines have a parametric definition. This means we have a
function/polynom of t that evalutes to x and y. x/y = f(t).

For our purpose we actually need the function y = f(x).
So as a first step we have to solve the solution x = f(t) for a given
t and then in a second step we evaluate y = f(t).

f(t) is a cubic polynom so we use cardanos formula to solve this equation
directly.

For the casus irreducibilis we need 3 functions that are a combination of
arcos and cos. Instead of evaluating arcos and cos we approximate these
functions directly.

TCB splines are converted into the corresponding cubic bezier spline.

Change-Id: Id2afc15efac92e494d6358dc2e11f94e8c524da1
Reviewed-by: Aaron Kennedy <aaron.kennedy@nokia.com>