Track Akismet spam checks, reflect on comment addition log #472

Fixes #472 by properly detecting Akismet response on new comments, and reflecting on new comment log `comment_type` added in #558. So users now should be able to filter auto-spammed comment easily.

@fjarrett @lukecarbis Please review/test.

/cc @krogsgard Can you [checkout this branch](https://github.com/x-team/wp-stream/archive/issue-472.zip) and confirm this solves your issue on #472 ?
@shadyvb Needs to be Yoda style