[neurun] Merge graph node classes (#2497)

[neurun] Merge graph node classes (#2497)

Merge Old Node into New Node.

Old Node : `internal::tflite::op::Node`
New Node : `neurun::graph::operation::Node`

- struct `Param` for each Node holds non-tensor parameters only
- Tensor parameters are stored in `_inputs` and `_outputs`
- Provide a default implementation of get/setters for inputs and
  outputs of `Node`
- `NodeVisitors` are now for New Node, not Old Node
- class `Linear` now holds New Node rather than Old Node

This commit completes the draft commit #2479, with #2483 and #2486
which were already merged.

Resolve #2404

Signed-off-by: Hanjoung Lee <hanjoung.lee@samsung.com>