Implement support for https connections

• Implemented connection to the node using the http (unsecured) protocol.
• Implemented https (secured) protocol in the cli_wallet.
• Implemented fc::mutable_url
• Improved fc::http_api_connection
• Implemented --skip-cert-check option cli_wallet option

Example usage:

cli_wallet -s"https://api.hive.blog"

Branch with tests: mzebrak/wallet-support-http-connection

Closes #168 (closed)