**Motivation**
In order to generate leads easily from survey submissions, we allow users to configure
a lead-generation option on answers of multiple choice questions. When selecting at least
one of those answers when taking the survey, use relevant information to generate a lead.

**Specification**
On such a submission, and only for a survey with type 'survey', 'live_session' or 'custom',
we create a lead:
- The lead's description is populated with the user's inputs. This is deemed sufficient
  and the link between the survey input and the lead is not stored directly in db;
- The customer field is set to the contact taking the survey. Otherwise, a nickname and/or
  an email question may be added to the survey to collect these user information if he is
  not logged in. If provided, the nickname's answer is set as the contact name field and in
  the lead title;
- The lead's medium is set as 'Survey' and the source as the survey title;
- The lead is assigned to the sales team provided, if there is one. The survey's responsible
  is set as the salesperson if he is part of the team, otherwise it is the team leader, or no
  one if there is no team leader.
Leads for a same survey are generated in batch.

**Other changes**
- New demo data 'Let's connect', a survey with some lead generating answers;
- New survey template 'Lead Qualification' that can be selected in the helper;
- New stat button 'Leads' on the survey;
- Slight display change for adding survey languages to allow the addition of a
  sales team field if at least one question can generate leads.

**Tests**
A few tests have been added:
- Logged in user answering survey, selecting lead-generating answers;
- Public user answering survey, selecting lead-generating answers, and
  with the survey responsible being in the sales team assigned to the
  survey.

task-4778192