Add file loading option to raspitexutil
Add missing files
Add shader loading option to RASPITEXUTIL_SHADER_PROGRAM_T: If the
shader definition string vertex_source oder fragment_source begins with "file:"
the variable will be interpretet as filename and the file will be
loaded. This decouple the shader definitions from the c code.

Add shaders: The pong applications contains three new shaders for
the camera texture: sobel, hsv (+linear transformation), and mirror.
The shaders are defined in apps/raspicam/shader/gl_scenes/

Add options: --pongCycleShaders and --pongUseShader [N]
The first option activate a cycling through the available shaders of
the pong app. The second option select one filter for the whole runtime.