Add journal entry to group page

[Kristina Hoeppner]

Discussion at https://mahara.org/interaction/forum/topic.php?id=6241&post=26463

Be able to add a journal entry from a user's personal journal to a group page (note: this is not the communal journal / blog bug #547332, but using existing private content to display in a group).

A few things would need to be figured out for this:
- Who can add a journal entry: Just the user themselves, the group admin (if the admin, how does that affect privacy)?
- Should journal entries also be added based on tags? If so, should all entries of all group members be displayed together or should you always have to choose the user?
- How is the author information displayed?