* constexpr ctor for EnumMask

* added pass properties to core passes.

* added unit tests.

* minor fixes.

* Reduce concat fusion test input sizes

* missed something

* [WIP] First commit

* Remove some commented code

* Further changes

* Further changes

* Add method to remove patterns with just one concat

* Add tests

* Add more tests

* Fix fan out case

* refactor code

* refactor code

* Added NGRAPH_DEBUG statements

* Use INTERPRETER as backend instead of CPU...travis build failure

* clang

* minor edit

* add more checks in the tests

* Incorporate Bob's comment

* Removed some NGRAPH_DEBUG statements and incorporated Pruthvi's comment

* Incorporate Xiaoyu's comments

* some refactoring