Add articleReply filter to ListArticles

[MrOrz]

According to meeting note, it would be great to have an advanced filter for article replies to track down blocked user's activities. It would also help profile page, when listing replies of the current user.

This PR adds filters to the following fields:

• Query.ListArticles
  • Adds articleReply.appId / userId / createdAt / selfOnly filter so that ListArticles returns only articles with article replies matching the specified filter.
  • Adds lastMatchingArticleReplyCreatedAt sorts articles using the latest articleReply's creation time matching the above filter
• Article.articleReplies
  • Adds appId, userId, selfOnly filters to filter article replies on server-side in application-level

[coveralls]

Coverage increased (+0.1%) to 87.467% when pulling cb167c719e5e51930733ed0a2ec50d79f6360042 on article-reply-filter into d806fc6f179aa68caf13f0b9cc54ebfc5f52cb37 on master.