Blogs: Tweak what happens when a post status is changed.

r8073 introduced bp_blogs_catch_transition_post_status() to determine
how blog posts are recorded in the activity stream.  However, blog
post edits are not accounted for.

This commit:
- Updates a blog post's activity item when a post is edited
- Mirrors a blog post's comment status to activitymeta for use with bp_blogs_comments_open() (see r8189)
- Removes the usage of bp_blogs_record_post() when a post has changed to an unpublished status.  bp_blogs_record_post() already fires on the 'delete_post' action, so this isn't necessary.  Instead, we remove the corresponding activity entry.

See #5333, #5130

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8191 cdf35c40-ae34-48e0-9cc9-0c9da1808c22