[uicfg] Fix autoform_section rtags wrt derivation cw 3.25 introduced the 'derived rtags' feature, but missed that `autoform_section` implementation was overriding several methods where this was implemented in the base class. The following problems are tested and fixed: * during init, we should not attempt to call `_initfunc_step2` if there is some parent, * but we should handle expansion of wildcard ('*' used as subject or object of a tag) since this is handled during init step for this class, unlike others which handle this in `get` method (i.e. at lookup time), * fix overrided `get` method to consider parent rtag if any. Closes #17107020

[rtags] Enhance repr of rtags * we don't care of the class, the registry id is enough (never seen a case of sub-classing) * add the module from which the rtag is coming as well as parent rtag if any.

[web/test] Use bare unittest main instead of lgc.main

[cleanup] Fix some flake8 errors and drop upper bound of copyright along the way. autoform module is not added to flake8-ok-files since there are some remaining errors to be handled, but that's still a start.

[doc] Update the advanced tutorial to follow the new style layout of cubes among others.

[views] Respond with 400 Bad Request in case of validation error in ajax request Previously, we raised a plain RemoteCallFailed without a status code, in which case it defaults to "500 Internal Server Error". Now, for validation errors, we issue a 400 Bad Request since these are clearly client errors.