1. Deprecate and remove Ubuntu16.04 base docker. Starting ROCm3.7 ROCm dropped Ubuntu16.04 support.
2. Add Ubuntu20.04 based develop dockerfile.
3. Explicit add symbolic link of "/opt/rocm --> /opt/rocm-3.7.0" in the CentOS based dockerfile
New dockerfiles exist in a subdirectory called /dev. These are
meant to serve as base docker images downstream dockerfiles
use in FROM statements
Fixed stale URL's and fixed up the name of the rocm kernel packages.