The scripting API is extended to support custom fragment shaders. To
support this a new method addFragmentShader is added taking ShaderTraits
and fragment shader. The GLShader is not exposed, instead a uint id is
provided which maps to the GLShader.

This shader id can be used in the animate and set calls to specify the
shader. The animation object is extended by the "fragmentShader" property.

The shader sources are located in the "shaders" directory of the package
contents.

E.g. the scale effect extended by the shader of the invert effect will
have the following layout:

   package/contents/
   -> code/
     -> main.js
   -> shaders/
     -> invert_core.frag
     -> invert.frag

The adjustment in code are:
 * in constructor to load the shader
    this.shader = effect.addFragmentShader(Effect.MapTexture, "invert.frag");
 * in animations objects of the slots the additions
   fragmentShader: this.shader
 * using the type Effect.Shader

or in full:

        window.scaleInAnimation = animate({
            window: window,
            curve: QEasingCurve.OutCubic,
            duration: this.duration,
            animations: [
                {
                    type: Effect.Scale,
                    from: this.inScale
                },
                {
                    type: Effect.Opacity,
                    from: 0
                },
                {
                    type: Effect.Shader,
                    fragmentShader: this.shader
                }
            ]
        });

The animation settings object supports a "uniform" value which takes the
string name of the uniform. For this uniform the location is resolved
and stored in the meta data of the AnimationEffect. This requires the
type Effect.ShaderUniform.

An example animation:

        window.scaleInAnimation = animate({
            window: window,
            curve: QEasingCurve.Linear,
            duration: this.duration,
            animations: [
                {
                    type: Effect.ShaderUniform,
                    fragmentShader: this.shader,
                    uniform: "uForOpening",
                    from: 1.0,
                    to: 1.0
                }
            ]
        });

Furthermore a new setUniform scriptable method is added to the
ScriptedEffect. This allows to update uniforms when the configuration
changes.

The call takes a generic QJSValue which supports:
 * float
 * array of 2, 3 or 4 components
 * string as color
 * variant as color

An example usage to read a color from the configuration and set it as a
uniform:

    effect.setUniform(this.shaderId,
                      "uEffectColor",
                      effect.readConfig("Color", "white"))