为了及时响应业务上线问题，先行合入

* add grid sampler

* reset act

* fix conflict and readme, test=develop

* fix ios v8 run error

* fix grid_sampler compute error. test=develop

* fix exp act run error, test=develop

* fix format, test=develop

* fix leakyrelu and tanh compute error, test=develop

* delete extra file, test=develop

* reset act

* fix conflict and readme, test=develop

* fix ios run error, test=develop

[LITE][OPENCL] support fp16 for cl_image_converter, layout, activation all OpenCL image kernel. test=develop (#2964)

* [LITE][OPENCL] support fp16 for cl_image_converter, layout, activation image kernel. test=develop

* add conv, depthwise and UT. test=develop

* add pool, conv, nearest_interp kernel. test=develop

* support fp16 for scale, reshape, concat, fc buffer opencl kernel. test=develop

* refactor for mul opencl buffer kernel. test=develop

* support fp16 for elementwise_mul opecl image kernel. test=develop

* support fp16 for elementwise_mul opencl image kernel. test=develop

* support fp16 for ele_add, fuse_ele_add_act opencl kernel. test=develop

* rename io_copy. test=develop

* mobilenetv1,v2 passed on 855. test=develop

* fix opt for opencl. test=develop