Merge pull request #15371 from Wenzhao-Xiang:gsoc_2019

[GSoC 2019] Improve the performance of JavaScript version of OpenCV (OpenCV.js)

* [GSoC 2019]

Improve the performance of JavaScript version of OpenCV (OpenCV.js):
1. Create the base of OpenCV.js performance test:
     This perf test is based on benchmark.js(https://benchmarkjs.com). And first add `cvtColor`, `Resize`, `Threshold` into it.
2. Optimize the OpenCV.js performance by WASM threads:
     This optimization is based on Web Worker API and SharedArrayBuffer, so it can be only used in browser.
3. Optimize the OpenCV.js performance by WASM SIMD:
     Add WASM SIMD backend for OpenCV Universal Intrinsics. It's experimental as WASM SIMD is still in development.

* [GSoC2019] 

1. use short license header
2. fix documentation node issue
3. remove the unused `hasSIMD128()` api

* [GSoC2019]

1. fix emscripten define
2. use fallback function for f16

* [GSoC2019]

Fix rebase issue

modules/core/src/parallel.cpp

@@ -54,7 +54,7 @@
 #endif
 
 #if defined __linux__ || defined __APPLE__ || defined __GLIBC__ \
-    || defined __HAIKU__
+    || defined __HAIKU__ || defined __EMSCRIPTEN__
     #include <unistd.h>
     #include <stdio.h>
     #include <sys/types.h>
@@ -793,7 +793,7 @@ int cv::getNumberOfCPUs(void)
 #elif defined __ANDROID__
     static int ncpus = getNumberOfCPUsImpl();
     return ncpus;
-#elif defined __linux__ || defined __GLIBC__ || defined __HAIKU__
+#elif defined __linux__ || defined __GLIBC__ || defined __HAIKU__ || defined __EMSCRIPTEN__
     return (int)sysconf( _SC_NPROCESSORS_ONLN );
 #elif defined __APPLE__
     int numCPU=0;