PURPOSE

Allow "free text" questions in the event questions asked to attendees, in
addition to the existing "selection" type.
e.g: "What are your allergies?"

Rework existing reporting on Questions to ease implementation and give more
meaningful answers analysis.

SPECS

**Free Text Questions**

The implementation is heavily based on the modelisation we chose for the survey
module since the features become similar in terms of question types and inputs.

- Introduce a 'question_type' that is either 'simple_choice'
  (= previous behavior) or 'text_box' that will contain the attendee text
  answer.
- Rename the event.answer model to event.question.answer to make it more
  obvious that it contains answer "suggestions" to a question of type
  'simple_choice'.
- Introduce a 'event.user_input.line' that is an answer to a specific question
  for a specific registration.
  It works very similarly to 'survey.user_input.line' but it's not contained in
  a 'user_input' model, it's directly linked to the registration using a
  'user_input_line_ids' o2m field.

The frontend view has been adapted accordingly to display either a selection
input or a textarea based on the question type.
The frontend orm processing now takes in both answer types (id of suggested
answer or text input).

On the backend side, views have been adapted to display event questions and
attendee answers in a more convenient and logical manner.

**Questions Reporting**

Based on latest testing, the reporting on event questions was completely
unusable if you have more than a hundred questions (all events combined) and
needs to be refactored based on new specifications.

We dropped the current reporting and re-introduced a new one after the commits
that let us handled free text questions.

The new reporting allow users to conveniently analyze attendees answers on a
per-question basis. It shows:
- A graph view showing counts of each suggestions for simple_choice questions
- A pivot view showing registrations vs answers for simple_choice questions
- A tree view showing textual answers values for text_box questions

FIXIMP

When changing the event.type, configured event questions that have answers
(type 'simple_choice') new have their answers properly copied onto the event.

LINKS

Upgrade PR odoo/upgrade#799
Task ID 2189529