* Refactor backend tests
* Rewrite reference implementation
* Align ref impl signature with order of inputs in v5
* Remove legacy code for training and backprop
* BarchNorminference operation class review
* Use reference to const in helpers to validate input shapes
* Refactor type_prop tests to cover v0 and v5
* Add type_prop tests
* epsilon attribute test with invalid value
* invalid integer input types
* Add serialization single layer test
* Add attribute visitor test
* Fix arm plugin test failure with dynamic element type
* Remove CoordinateTransform index call
* Add attribute count to visitor test
Number of ops went down by 4.
Also fewer floating point operations improves precision here, so we're able
to unblock some test cases from ngraph's suite.
Gabriele Galiero Casay