Remove QTKit for Xcode 8 / macOS 10.12 Sierra

[jdonald]

QTKit was deprecated some time ago and then removed altogether in favor of AVFoundation.

Fortunately this didn't require too many drastic changes. I just kept looking at the modified method signatures across AVCaptureDeviceInput, AVCaptureSession, and other classes while making appropriate tweaks.

• Fixes QTKit not available anymore on macOS Sierra #27
• Fixes Failed building #30
• Falls back to cammacos when OpenCV is not found
• Installs camopencv without cammacos when OpenCV is found

I tested this on my MacBook running Sierra. Although I'm unable to easily run the standard sanity-test camera.testme() due to its dependence on qtwidget/qtlua -> Qt 4, I did a full test with torch + a browser + my built-in webcam using vfonov/deep-pi modified for macOS.

It was only after going through most of this exercise did I realize that when OpenCV is available, one can run on Sierra with the entire camera.m implementation omitted. I have tweaked the CMake configuration to make it install with only one or the other (camopencv or cammacos), but not both.

If you build OpenCV locally, note that at a minimum it requires configuration settings such as -DBUILD_opencv_objdetect:BOOL=ON -DBUILD_opencv_photo:BOOL=ON -DBUILD_opencv_video:BOOL=ON -DBUILD_opencv_videoio:BOOL=ON and headaches are likely minimized via -DBUILD_SHARED_LIBS:BOOL=OFF.

[susiefu]

This worked great, thanks @jdonald!

For everyone still with issues in #27 and #30, check out this unmerged pull request and make the rock locally

git fetch origin pull/31/head:fix-avfoundation
git checkout fix-avfoundation
luarocks make camera-1.1-0.rockspec