Adding uint8 support for squeeze operator.

* Add double grad in Squeeze and Unsqueeze

* Add double grad in Squeeze and Unsqueeze

enhanced ops: unsqueeze, squeeze2, strided_slice, unsqueeze,
unsqueeze2, var_conv_2d, spectral_norm, slice, match_matrix_tensor,
nce, pad, pad_constant_like, filter_by_instag

* fix input shape of op tests for elementwise_sub,
gather, pad2d, transpose, softmax, scale,
elementwise_max, hierarchical_sigmoid, reshape2,
sign, squeeze, reduce_sum, sum, squeeze2,
unsqueeze, unsqueeze2, cast, reverse

test=develop

* fix cast, elementwise_mul, gather, scale, sign,
softmax, transpose

test=develop

There are PythonAPI tests in Op's unittest which don't need to inherit OpTest class.

* improve unsqueeze op to support int, Tensor and Tensor list for argument axes.
test=develop

* call Resize only when necessary. test=develop

* add kernel for unsqueeze_op, test=develop

* add kernel for unsqueeze_op, test=develop

* add kernel for unsqueeze_op, test=develop

* Add intermediate

* fix flatten/squeeze/unsqueeze

* Considering compatibility issues, we could not fix the origin op

* follow comment

* reset the shape of XShape