### Description / Overview We want to support the correction of Jupyter notebooks for Python exams. In order to that with our current interface we convert the Jupyter notebook into a Python script with comments describing where each cell starts and also comment blocks after each input with the corresponding cell output. Because we want the tutors to have the ability to look at the original notebook in case there are things missing in our script representation (we don't render images). Since the conversion happens in hekctor and not in the backend/frontend we need to store the original `.ipynb` as well as the rendered version. grady-corp/rusty-hektor> already supports this rendering of `.ipynb` notebooks and places it in the normal `code` field. The original `.ipynb` is placed under the `source_code` field. ### Use cases (Who is this for?) ### Links / references ### Feature checklist So in order to fully support Jupyter notebooks, the following things need to be done: **Backend** * [x] add a nullable `source_code` field to the `Submission` model * [x] add a boolean `source_code_available` field to the `Submissions` * [x] add this field to the views where needed * [x] add a route to the submission view that returns a corresponding `source_code` if available **Frontend** * [x] add the optional `sourceCode` field to the `Submission` model(s) * everywhere student submissions are displayed (don't forget Student views!): * [x] if `sourceCodePresent` is true, show `Download original source` button in top toolbar * [x] when `Download original source` is clicked, fetch source from backend