8-bit bit planes view for QCView

Previously, the bit planes view defaulted to a view of 10 bit positions (rendered as columns of image and numbers), which meant that if you were transferring at a bit depth of 8, you would see 8 bits' worth of image and 2 blank bits.

#319 changes bit planes so that it only shows 8 columns if you're transferring at a bit depth of 8, but this change only works for playback views that use ffplay. It would be great to have this functionality in QCView/mpv playback and prevent misunderstandings about bits being thrown away.

I am currently trying to work with `MPVOPTS+=(--script-opts=qcview-pixelformat="${PIXEL_FORMAT}")` over at the [bitplanes-qcview](https://github.com/aeschweik/vrecord/tree/bitplanes-qcview) branch.