Add controls for image effect parameters

[waveform80]

As per this forum post from 6by9 (former post has structure required)

[waveform80]

This seems rather buggy. In 6by9's post the maximum number of parameters is 6, but the MMAL headers define MMAL_MAX_IMAGEFX_PARAMETERS as 5. After attempting to query parameters for an active effect with MMAL_PARAMETER_IMAGE_EFFECT_PARAMETERS, we seem to get garbage back in the MMAL_PARAMETER_IMAGEFX_PARAMETERS_T struct; the mp.effect field is random, yet num_effect_params and the effect_parameter array always seem to be 0. Furthermore, the query seems to lock up the camera requiring a reboot (a second query simply doesn't return); nothing pertinent in the vcdbg log either.

For now, I'll remove this from the 1.7 target and come back to it when I can figure out either what I'm doing wrong or whether this is really an upstream bug.

[waveform80]

Ah ha! Getting parameters is only possible after a successful attempt to set them, as detailed in 6by9's forum post. Must test whether it's possible to set invalid nonsense as well as we should throw an exception if the user attempts to set silly things.