Supporting double majors

[rbenjos]

Is your feature request related to a problem? Please describe.
As of the moment, we only support students with one major. (like CS alone)
However, a substantial number of them combine two majors, and sometimes even more.
I think we should consider how to support these cases.

Describe the solution you'd like
The rules of combining more than one major are not very simple, but they are programmable.
Courses which must be taken still get a priority over choice courses.
This would require the backendend developers to add an additional module to combine different course groups
From different tracks.

On the FE side it would require little to no work, as it would only require adding another dropdown menu for the second track.