- improve cpu dispatching calls to allow more SIMD extentions
    (SSE4.1, AVX2, VSX)
  - wide universal intrinsics
  - replace dummy v_expand with v_expand_low
  - replace v_expand + v_mul_wrap with v_mul_expand for product accumulate operations
  - use FMA for accumulate operations
  - add mask and more types to accumulate's performance tests

  - redefine 16-bit multiply operator to perform saturating multiply
    instead of non-saturating multiply
  - implement 8-bit multiply operator to perform saturating multiply
  - implement v_mul_wrap() for 8-bit, 16-bit non-saturating multiply
  - improve performance of v_mul_hi() for VSX
  - update intrin tests with new changes
  - replace unv 16-bit multiplication operator with v_mul_wrap due behavior changes

  - Several improvements depend on vpisarev review

    * initial forward declarations for universal intrinsics
    * move emulating SSE intrinsics into separate file
    * implement v_mul_expand for 8-bit
    * reimplement saturating multiply using v_mul_expand + v_pack
    * map v_expand, v_load_expand, v_load_expand_q to sse4.1
    * fix overflow avx2::v_pack(uint32)
    * implement two universal intrinsics v_expand_low and v_expand_high

* Add Squeezenet support in ONNX

* Add AlexNet support in ONNX

* Add Googlenet support in ONNX

* Add CaffeNet and RCNN support in ONNX

* Add VGG16 and VGG16 with batch normalization support in ONNX

* Add RCNN, ZFNet, ResNet18v1 and ResNet50v1 support in ONNX

* Add ResNet101_DUC_HDC

* Add Tiny Yolov2

* Add CNN_MNIST, MobileNetv2 and LResNet100 support in ONNX

* Add ONNX models for emotion recognition

* Add DenseNet121 support in ONNX

* Add Inception v1 support in ONNX

* Refactoring

* Fix tests

* Fix tests

* Skip unstable test

* Modify Reshape operation

* may be an typo fix

* remove identical branch,may be paste error

* add parentheses around macro parameter

* simplify if condition

* check malloc fail

* change the condition of branch removed by commit 3041502861318c85d901e8c08226ff67898c77ed

* simplify condition

* dims must > 0 or latter sz[dims-1] will underflow

* rewrote Mat::convertTo() and convertScaleAbs() to wide universal intrinsics; added always-available and SIMD-optimized FP16<=>FP32 conversion

* fixed compile warnings

* fix some more compile errors

* slightly relaxed accuracy threshold for int->float conversion (since we now do it using single-precision arithmetics, not double-precision)

* fixed compile errors on iOS, Android and in the baseline C++ version (intrin_cpp.hpp)

* trying to fix ARM-neon builds

* trying to fix ARM-neon builds

* trying to fix ARM-neon builds

* trying to fix ARM-neon builds

* trying to fix the custom AVX2 builder test failures (false alarms)

* fixed compile error with CPU_BASELINE=AVX2 on x86; raised tolerance thresholds in a couple of tests

* fixed compile error with CPU_BASELINE=AVX2 on x86; raised tolerance thresholds in a couple of tests

* fixed compile error with CPU_BASELINE=AVX2 on x86; raised tolerance thresholds in a couple of tests

* seemingly disabled false alarm warning in surf.cpp; increased tolerance thresholds in the tests for SolvePnP and in DNN/ENet

POD structures can't have constructors.

* Remove a forward method in dnn::Layer

* Add a test

* Fix tests

* Mark multiple dnn::Layer::finalize methods as deprecated

* Replace back dnn's inputBlobs to vector of pointers

* Remove Layer::forward_fallback from CV_OCL_RUN scopes

Signed-off-by: Zhenqing Hu <huzq85@gmail.com>