Use 451 as the target framework for full CLR when packing

#331
Use new logic to fetch default author

- If author is not specified in project.json and there is a non-empty env var named "K_AUTHOR", we use its value
- Use project name as the final fallback when there is no default author
Add proxy support in kvm

- Add proxy option to "kvm upgrade"
- "kvm upgrade" uses global proxy (http_proxy env var) by default
- Support authenticated proxies