- support only one stem in model
- enable model init strategies

- Output node is vertex_op(sum(edges)) + projected input
- Yaml:
    - every cell reduction, cell stem = max_pool, model stem
    - Model desc: model matrix, vetex ops
- Do we need alphas?
- Do we need to modify finalizers?
- Ops() overriding in NasBench101Op
- Do we need to specify children in OpDesc?