ToS acceptation

[lbesson]

This is a follow up of the backend part: c2corg/v6_api#1542

When the user logs in in the UI, and if the ToS are not accepted, a 403 will be returned with the body 'Terms of Service need to be accepted'

In that case, the UI should re-display the login form with a tickbox for accepting terms of conditions, and all 3 fields (login, email and tickbox) must be sent to the backend so that the ToS acceptation is stored in the db. Next logins will not get the 403.

Note: the backend part has not been merged yet. Please see with developers in order to enable this for demo if you start working on it, or run the branch of the backend locally.

[florentcadot]

Here is one attempt to solve this issue: #3838