G-API: add transformation logic to GCompiler

* Introduce transformation logic to GCOmpiler

* Remove partialOk() method

* Fix minor issues

* Refactor code according to code review

1. Re-design matchPatternToSubstitute logic
2. Update transformations order
3. Replace check_transformations pass with a
   one time check in GCompiler ctor

* Revert unused nodes handling in pattern matching

* Address minor code review issues

* Address code review comments:

1) Fix some mistakes
2) Add new tests for endless loops
3) Update GCompiler's transformations logic

* Simplify GCompiler check for endless loops

1. Simplify transformations endless loops check:
 - Original idea wasn't a full solution
 - Need to develop a good method (heuristic?) to find loops
   in general case (TODO)
2. Remove irrelevant Endless Loops tests
3. Add new "bad arg" tests and unit tests

* Update comments

This is useful for bidirectional LSTMs.

Fix computation of internal shapes in Deconvolution layer

* Fix computation of internal shapes

* Refactoring

to control CL_MEM_USE_HOST_PTR usage

- avoid data copying after buffer block shrink
- resize current block in case of single FileNode

[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

ea3dc789
https://github.com/opencv/opencv_contrib/commit/83fc27cb99db4435d07974090fbdc77d831931cd

Fix documentation

* 3rdparty: libpng v1.6.37 MSA patch (pr15422)

original files: https://github.com/glennrp/libpng/tree/v1.6.37/mips

* 3rdparty: libwebp MSA asm patch (pr15422)

* Added MSA implementations for mips platforms. Intrinsics for MSA and build scripts for MIPS platforms are added.
Signed-off-by: Fei Wu <fwu@wavecomp.com>

* Removed some unused code in mips.toolchain.cmake.
Signed-off-by: Fei Wu <fwu@wavecomp.com>

* Added comments for mips toolchain configuration and disabled compiling warnings for libpng.
Signed-off-by: Fei Wu <fwu@wavecomp.com>

* Fixed the build error of unsupported opcode 'pause' when mips isa_rev is less than 2.
Signed-off-by: Fei Wu <fwu@wavecomp.com>

* 1. Removed FP16 related item in MSA option defines in OpenCVCompilerOptimizations.cmake.
2. Use CV_CPU_COMPILE_MSA instead of __mips_msa for MSA feature check in cv_cpu_dispatch.h.
3. Removed hasSIMD128() in intrin_msa.hpp.
4. Define CPU_MSA as 150.
Signed-off-by: Fei Wu <fwu@wavecomp.com>

* 1. Removed unnecessary CV_SIMD128_64F guarding in intrin_msa.hpp.
2. Removed unnecessary CV_MSA related code block in dotProd_8u().
Signed-off-by: Fei Wu <fwu@wavecomp.com>

* 1. Defined CPU_MSA_FLAGS_ON as "-mmsa".
2. Removed CV_SIMD128_64F guardings in intrin_msa.hpp.
Signed-off-by: Fei Wu <fwu@wavecomp.com>

* Removed unused msa_mlal_u16() and msa_mlal_s16 from msa_macros.h.
Signed-off-by: Fei Wu <fwu@wavecomp.com>

* remove old BUILD_opencv_java option

* replace old build_java option with new BUILD_JAVA option