Delete the semester model
The semester information can be de-normalized to simplify the architecture.
To ease some manipulations, replace it in all models by two fields one year (4 digits) and one enum with "P" (spring) or "A" (autumn) possible values.
Make sure to update the reducers and viewsets as necessary.
And to update the API
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information