show default fieldsets

Originally submitted by Nathan Hwang - Added a visible attribute to
fields.  

Allows admins to choose if fields display or not: useful if
some field is uninformative to everyone but the admins. 


### To Update database after applying changes (this needs to be tested):

in the rooibos directory:

    python manage.py schemamigration data --add-field='field.visible'

or

    python manage.py schemamigration data --auto

and then

    python manage.py migrate data