* straightforward gpu.cos implementation following previous patterns prior to refactor

* Generalized unary elementwise gpu op impl.. New unary elementwise ops can
be added to the type annotations in gpu_cuda_kernel_ops.hpp. Next step
is to refactor the llvm interface in gpu_emitters.hpp for similar generality.

* Added gpu_emitter.hpp:EmitUnaryElementwise.

Function adds cuda kernel based on ngraph::op::op_type::description.
This can service all unary elementwise ops run on the gpu.

* The following elementwise unary ops now use the EmitUnaryElementwise emitter:
* GPU.abs
* GPU.acos
* GPU.asin
* GPU.atan
* GPU.ceiling
* GPU.cos
* GPU.cosh
* GPU.exp
* GPU.floor
* GPU.log
* GPU.not
* GPU.sign
* GPU.sin
* GPU.sinh
* GPU.tan
* GPU.tanh
Unary elementwise ops Sign and Not need extra consideration.

* tanh test changed to test::all_close for fp comparison (also done for tan in commit 65fa7c6de34c8277fe2a4801644f6bb64574f4ff).

* GPU backend skips added for recent softmax test and updated aliased output test that uses op::Constant.

* code format update

* changed cuda builder interface names to unary/binary/arbitrary, added impl. note to gpu_cuda_kernel_ops, cleaned code format

* updated ngraph-cpp reference

* Fixing incorrect github conflict resolution.

* Added GPU emitter for op::Result.
For now it simply copies the output tensor.

All but 3 tests now pass. The remaining
failing tests are:
* GPU.dot_0_0
* GPU.dot_matrix_2x0_0x2
* GPU.dot_2x0_0

* Removed call to handle memory aliasing in gpu_external_function.

* fix gpu emitter bug that will return in the middle of function

* Merge pull request #609 from NervanaSystems/tfl/fix_return_bug

fix gpu emitter bug that will return in the middle of function

* GPU backend skips added for recent softmax test and updated aliased output test that uses op::Constant.