Feat: added task lifecyle events to Linguo

[hbarcelos]

Motivation

Currently we don't have a timeline of the main events of the lifecycle of a translation task.

So far I identified the following use case:

• When displaying resolved tasks in the UI, we should sort them by descending completion date to give a feel of 'liveness'.

Another possibility would to display the task lifecycle in the UI or collecting metrics to perform data analysis like "how much time in average does it take to a task to be completed?"

This is an alternative to #309.

Proposed Changes

• Add a TaskResolved event to allow knowing when and why the task was marked as resolved.
  • The reasons why a task might've been marked as resolved are:
    1. The translation was accepted by the requester.
    2. The requester was reimbursed either because no translator assigned to the task or a translation was not submitted within the time window.
• Add a TranslationChallenged event to allow knowing when the translation was challenged and who made the challenge.
  3. The translation was challenged, judged and the ruling was applied by the arbitrator.
• Add a timestamp param to both TaskCreated and TranslationSubmitted events to have a "persistent" registry of their values, because task lastInteraction is mutable.

Risk Analysis

No code changes were made beyond adding/modifying events.