install opencv3 into openframeworks, once and for all

opencv library comes separately, so whenever opencv is required for an OF project, we need extra setup.

Now, this is a one-time set-up method.

1. install opencv library somewhere like '/usr/local'. You need to make a static library! Then, combine all the static libraries into one file: libopencv.a
2. copy the header files and library into $OF/libs/opencv/include and $OF/libs/opencv/lib
3. edite CoreOF.xcconfig in the openframeworks folder, or you can find it in xcode by opening any example project.
4. done.

If you have a dynamic libraries, do the above only for include files. Libraries are included in your project through the xcode-project. Make 'New Group' and put all the dynamic libraries; they will be linked automatically during the Build time.