* nG Python api for Gather and IE IR reader tests
* also included old IE IR reader test for Gather1
* added a blank line before Gather
* style corrections
* applied review comments
* removed blank line
* removed xfailed for Gather7 with batch_dims since CPU was moved to nGraph (...allows to fallback node execution on ngraph evaluate() method in case if optimized implementation is absent)
* added new visitor tests
Pavel Esir