[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.

[sources] Enhance prototype of check_conf_dict * mark it private * explicit name * update docstring Private function is still called from syncsources but this will be updated in a follow-up.

[sources] Stop translating validation error this should be done later in the web ui, where lang is properly set.

[sources] Simplify source's init method Only call it when enabled instead of giving a boolean flag indicating whether it is or not (which were not correctly considered).