subreddit macroPlaceholder returns subreddit of current thing, or current subreddit if not explicit
reply_to macroPlaceholder returns subreddit of current thing, or current subreddit if not explicit
refactor RESUtils.subredditForElement from commentTools.magicPlaceholders for subreddit
RESUtils.subredditForElement also looks for subreddit in closest tagline or for the first/only link on page
Merge pull request #1749 from andytuba/macroplaceholder-outsidecommentpages

{{subreddit}} and {{reply_to}} macro placeholders work when not in comments page