Purpose of this commit is to polish a bit this old module before working
on it. Contains
* split python model into separate main files to ease models understanding;
* split views into separate main files to ease views finding;
* move data lost in views to data files (server action notably);
* merge templates in the same file to have all available at hand;
* move assets in their own file in order to remove noise from templates;
No functional behavior change should occur with this commit. Only move
has been performed.
This commit is linked to task ID 1903617 and PR #28166.
