Details:
Extend database structure, so that a task id can be mapped to a project id.
Tasks:
[ ] tasks can be re-assigned to different projects (db modify)
[ ] tasks with no assigned project are automatically put inside the "Inbox" in the frontend - for the backend, it will probably be sufficient to allow tasks with no assigned project --> these tasks will then be put in the "Inbox", which acts as a virtual project.
subtask of #5
Details: Extend database structure, so that a task id can be mapped to a project id.
Tasks: