* unique op for cuda is added

* add support for cuda

* Add cuda support for unique op.

* Add support for int32_t and int64_t.

* For old version, process by cpu

* Add VisitDataType for thrust

* update doc, test=document_fix

* add attr(dtype)

* refine code

* add unique_v2 op

* remove unique_v2 op

* update doc

Those ops include，scale， sum， sums，unique_with_counts，unique，
wherre， add error message and test case

* fix the device supported of the op unique and unique_with_counts.
test=develop
test=document_fix

* Fix the precision of test in the op of unique and unique_with_counts.
test=develop
test=document_fix