Draft: Refactor HTTP client and remove DNS lookup on start

Changes

• Use new client library in common-src (oai-cn5g-common-src!18 (closed))
• Remove curl_multi stuff from smf_sbi

Fixes

Fixes issues #27, #29 (closed), #5

@arora this MR removes the DNS lookup on start, users can just configure IP address or host and it is either resolved or not, it works for both.