Class announcements

[krishnans2006]

Adds functionality for:

• Class groups with a static message
• A global group
• Announcements sent in a group
• Hoco admin role to manage the hoco site (without superuser perms - e.g. sga)
• Class group admin to manage class group message/announcements (e.g. class council)

Still needed:

• Manage class groups without using Django admin
• Manage hoco admins and class group admins without Django admin

[alanzhu0]

Very good work in general implementing this functionality. See comments in files.

I have one major architecture comment regarding your ClassGroup model. This implementation seems very "hacky" to me, with the check for the username prefix and "_" for everyone. I would suggest you replace this using Django's built-in Group model and rewrite the logic accordingly. In addition, whenever a user logs in, the following pseudocode could be executed:

group = Group.objects.get(name=user.graduation_year)
if not group.exists():
    Group.objects.create(name=user.graduation_year)
else:
    if group not in user.groups().all():
        user.groups.add(group)

This would also allow for custom groups consisting of certain groups of users, such as SGA or CC. This also removes the need to manually add class groups every year.

Please also squash your commits to preserve only those with clearly defined feature additions.

[krishnans2006]

I am merging this PR now since the proposed architecture is simple to migrate to and is not affected by the current deployment implementation.

Further changes to the features implemented in this PR will be made directly to the master branch.