fix most recent post stolen by the last logged in user AND only show active users in post-settings-menu drop-down

fixes #3549 fixes #3528
- instead of grabbing and setting the author after fetching the list of users, get the author info from the models "author" property and set it when that value returns. (3549)
- added filter to the PSM's "authors" attribute to only display active users (3528)
Merge pull request #3569 from morficus/issue-3549

fix most recent post stolen by the last logged in user AND only show active users in post-settings-menu drop-down