Add status field based on seat numbers

[Bad-Science]

As per YACS-RCOS/university#8, we want to add a status field to sections at RPI in order to be consistent with NYU. In the case of RPI, we track the fields seats and seats_taken, where seats is the total number of seats in a section, and seats_taken is the number of students that are currently registered for the section.

The status field for each section should be set based on the following conditional:

if seats_taken >= seats
  status = 'closed'
else
  status = 'open'
end