[SSF] Members for tasks

Added an "Interested" field that would show up in the rheader/form for Tasks, and users can 'Watch' a task(i.e, assign themselves a 'following' role). However, deployment settings can be changed to allow Users to assign themselves other roles such as "Mentor", "Volunteer" that shows up as a dropdown-list along with the "Watch" button.

No, those are different:

    if activity:
        activity = TR(TH("%s: " % T("Activity")),
                             activity.name
                             )
    else:
        activity = ""

No repitition here.

Compare to yours:

    if record.created_by:
        creator = TR(TH("%s: " % T("Created By")),
                             s3_auth_user_represent(record.created_by),
                             )
    else:
        creator = TR(TH("%s: " % T("Created By")),
                             "-"
                             )

...which repeats both the T() and the HTML layout.