[graph] Migrate to graph core

[graph] Migrate to graph core

Migrate neural network independent and generic sections of the graph
to graph core. This is not yet complete and will be done over a few commits.
This will cleanup NetworkGraph class and will allow optimizations to
be done on the GraphCore/NetworkGraph class easily, and simplify
the classes as well.

Now, graph related structures can move out from layer to layer node.

**Self evaluation:**
1. Build test: [x]Passed [ ]Failed [ ]Skipped
2. Run test: [x]Passed [ ]Failed [ ]Skipped

Signed-off-by: Parichay Kapoor <pk.kapoor@samsung.com>