Getting layer inputs (#1006)

They are initialized only in functors, not in inherited fields.

moved BLAS/LAPACK detection scripts to the main repository. Give preference to the external BLAS over OpenCV's gemm, which improves performance of dnn module by a lot

fixed some compile warnings in dnn & protobuf; improved convolution layer performance when blas is not available by parallelizing gemmCPU() function in dnn

Also, small fix inside inside Python types conversion was added