WIP: Groups.  Can show group page, and group posts.  No posts are connected to groups yet, though.  No group members or group admins.
Parse group identifiers out of post text, and associate with groups.
Whitespace cleanup.
Restrict group posting to members only.
Group list.  Create group.
Edit and update groups.
General beautification of group page.
Don't allow creation of groups with invalid identifiers.
Buttons to edit a group and cancel editing.
Ability to remove members from a group.
Ability to add new members (space- or comma-separated ID list).
Tablify member list in group edit page.
People can now join groups themselves (without admin).  Admin gating forthcoming.
Beautification of group edit page.
Basic operations for group membership requests.  Request to join, listing, approval.
Reject group membership requests.
Set group admission policy from group edit page.
Set group admission policy on creation.
Disable join button depending on membership request status and admission policy.
Mark TODO for notifications re: groups and membership.