[entities] Fix backward compat of IDublinCore adapter wrt dc_long_title `entity.dc_long_title()` used to fallback to `dc_title()`, and most entity types were relying on this, thus only implementing the later. Since introduction of the IDublinCore adapter, if one call `entity.dc_long_title()` on an entity that only implements `dc_title()`, it will retrieve the adapter which will then call its own `title()` method instead of the `dc_title()` method of the entity as expected. Fix this by calling instead `entity.dc_title()` which will eventually kick in the backward compat layer if necessary.

[web] Do not try to rmtree symlinks in rmtreecontent() There is a symlink in data directory (created by generate_static_dir() method) and trying to rmtree() it will fail with an OSError. So we unlink() it instead.

[pkg] Version 3.25.0rc3

[test] Stop using lgc.testlib

Fix some flake8 errors

[sources] Turn classmethod into standard method No need for a class method and easier to get proper logger including source's name.

[test] Add some tests for hooks.syncsources for parts which are not located in some source's check_config / check_urls method.

[sources] Check source's url attribute value on creation/modification Similarly as for config. Now, ldap source validation is properly done there instead of at initialization time.

[sources] Check sources configuration is fine on creation/modification Reintroduce usage of 'source.check_config' which had almost disappeared, as well as tests for the currently detected errors. Part of the system source specific checking done in syncsources reimplemented in a specific check_config implementation. Tests are dispatched among ldap / datafeed and syncsources tests but are not strictly correctly located (notably syncsources tests behaviour of the native source's check_config). The system source url checking part which disappears from syncsources will be reintroduced in a follow-up.

[test] Fix option name in ldap wrong group test which wasn't actually testing what it expected (and nothing guarantee it does now, but that's another story). Fixing this will avoid failure once we properly check the configuration.