Feature/priority voting

[pabpercab1]

The purpose of this pull request is to introduce the functionality for a new priority-based voting system in Decide. Before executing the application or conducting tests, please follow these steps:

pip install -r requirements.txt
python manage.py makemigrations
python manage.py migrate

Given that the frontend interface for this feature hasn't been developed yet, testing will be performed through unit tests.

Key Changes and Concepts:

Used the multiple option voting structure: This new priority voting model is integrated in the current 'question_type' attribute.

Frontend Vote Format: For single-option voting, the format of a vote from the frontend is: vote: { "a": int, "b": int }. In contrast, for priority voting, the format is: vote: [ { "a": int, "b": int, "p": int }, ...]. The priority vote is structured as a list of dictionaries to ensure encrypted votes with chosen options reach the backend for decryption.

Implementation of the New Model in the Mixnet: Previous models (e.g., simple voting or multi-option voting) only consist of 'a' and 'b' parameters, while the priority voting requires an additional parameter ('p') to store the priority of the voted option.

White voting: Currently, it is not feasible to select white voting alongside priority voting due to the inherent contradiction. Allowing a combination of white voting with priority voting would undermine the purpose of the priority voting system. As such, it remains incompatible as it contradicts the nature of prioritizing and ranking options.

If you have any suggestions on how to enhance this feature or if you encounter a bug, please let me know!

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.20%	✅ 92.08% (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (2678a18)	3071	2729	88.86%
Head commit (a8e6019)	3208 (+137)	2857 (+128)	89.06% (+0.20%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#61)	202	186	92.08%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[marnunrey2]

Everything looks fine and working. Good job!