Add namespace sub-command for managing namespaces with faasd and OpenFaaS for Enterprises

Changelog for 0.16.15:

• PR #976 Implement namespace support using go-sdk by @nitishkumar71

Commits
ab72021 Fix test for lowercase error by @alexellis
b102982 Rename temp directory for fetching templates by @alexellis
93037de Update namespace descriptions and remove ioutil by @alexellis
03fd309 Implement namespace support using go-sdk by @nitishkumar71

Changes: 0.16.14...0.16.15

Generated by Derek