Added current_user_can( 'edit_comment', $comment_id ) to ajax moderation functions

Partial fix for:

https://github.com/GigaOM/gigaom/issues/5236

The JS is still not functioning correctly.

i.e. Clicking the moderation links doesn't seem to be triggering any JS at all it's just going to the link.  Possibly a related check somewhere in the JS?