* wip

* interperter use switch instead of if/else

* more cleanup

* make nop elimination run on all backends

* revert

* use single include file to define all ops so there is only one instance

* move op.tbl to ngraph/op dir as it is useful. Added useage example.

* add some comments where needed

* revert some changes to reduce delta

* add const

* add more const

* simplify using NodeWrapper

* update per review comments

* update per review comments

* update per review comments

* remove switch warning as it is not supported in older gcc