Backend API proposal

[effa]

Rules:

• always use full urls (e.g. 'task/ladder' or 'task-session/245' instead of just entity IDs)
• new session is only created if the last interaction is more than 1 (?) hour old
• snake_case identifiers, kebab-case values and urls
• only post actions (this is to make sure that all actions are processed by the core, but there might be some meaningful exceptions to this rule)

API:

• POST /api/action
  • {type="start-session"} -> {..., student}
  • {type="start-task", task} -> {..., task_session}
  • {type="see-instruction", instruction}
  • {type="solve-task", task_session}
  • (more actions in future, e.g. execute-program, change-program)
  • (this is the recommended way for REST to deal with model inheritance)
• GET /api/categories (with nested toolboxes)
• GET /api/tasks/:id
• GET /api/students/:id (with seen instructions, credits, level, recommendation + get_practice_overview detail route)
• GET /api/students/:id/practice-overview -> {tasks: [{url, category, solved, best_time}]}

[effa]

Implemented and tested