Add operators: `gemm` and `add` (#621)
Add operators: `gemm` and `add` (#621)

* add gemm

* update

* add

* add more checking for set_weights

intel-analytics/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL