GSoC 2017: Improve and Extend the JavaScript Bindings for OpenCV (#9466)

* Initial support for build with emscripten

mkdir build_js
cd build_js
cmake -D CMAKE_TOOLCHAIN_FILE=/path/to/emsdk/emsdk-portable/emscripten/master/cmake/Modules/Platform/Emscripten.cmake -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX=/usr/local ..

* Add js module

The output is build/bin/opencv_js.js

* Fix opencv2/calib3d.hpp not found issue

* Add module name

Usage:
var cv = cv();

* Add total memory as 128MB and allow growth

* Add compilation flags for emscripten

* Use EMSCRIPTEN build target

* Disable js module for non emscripten build

* Bind the preload file path to root

Usage:
face_cascade.load('haarcascade_frontalface_default.xml');

* add test folder

* fix test files

* Copy js module test to bin

* Support to run tests on Node.js

Fix tests to import cv Module when runtime is node.
Add tests.js to use qunit to auto run tests....