Use WP native functions wp_remote_(get|post) to make API calls

[meloniq]

Use WP native functions wp_remote_(get|post) to make API calls, instead of the custom dsq_ulopen() function.

Todo: remove or deprecate following functions which are no longer used:

• dsq_urlopen()
• _dsq_curl_urlopen()
• _dsq_fopen_urlopen()
• _dsq_fsockopen_urlopen()