Remove dependency on opencv4nodejs and CMake

[arnaudh]

## Problem

Depending on opencv4nodejs means the extension takes a long time (20 minutes+) to build, and the build itself is brittle due to the use of CMake (which is only needed to build opencv4nodejs).

Solution

MagicCardZoom only depends on opencv4nodejs for offline tasks such as indexing the images, however it is not used by the extension when running in the browser (since it is a NodeJS package).

In theory we could replace all usages of opencv4nodejs with calls to opencv.js (see my instructions here on how to compile any function from OpenCV), or other more lightweight image libraries. This way we can drop the dependencies on opencv4nodejs and CMake, and make the build faster and more robust.

[arnaudh]

Usages of opencv4nodejs:

- cv_debug.js
  - index_images (+ benchmark + contour_finder_test)
    - cvDebug.imread
      - **cv.imread**
    - cvDebug.resize
      - **img.resize**
    - cvDebug.cropToArtPlusOrbBorderInside
      - .crop
        - **img.getRegion**
        - **cv.Rect**
    - **img.gaussianBlur**
    - **cv.Size(1, 1)**
    - cvDebug.toImageData
      - **img.cvtColor**
      - **cv.COLOR_GRAY2RGBA**
      - **cv.COLOR_BGR2RGBA**
    - imwrite
      - **cv.imwrite**
  
  - [debug only: additional] identify_service + matcher
    - cv_debug.setDescriptorInputImg
    - cv_debug.fromImageData
      - **cv.Mat**
      - **cv.COLOR_RGBA2BGR**
    - cv_debug.drawAndSaveMatches
      - drawPoints
        - **cv.Vec**
        - **img.drawCircle**
        - **cv.Point2**
      - joinImages
        - **img.copyTo**
    - cv_debug.drawAndSaveContour
      - drawContour
        - **cv.Contour**
        - **img.drawContours**

So only 10 simple OpenCV functions/structs are essential.