[server] Move "system" source initialization into its own method

[entities] Make CWSource's dictconfig method clearer

[entities] Move CWSource update_config method as a function in 3.15 migration script This script is the only caller of this method. In the code of the function, drop "skip_unknown" argument and continue accordingly upon OptionError.

[server/test] Turn "pull" method of LDAPFeedTestBase into a staticmethod Because it does not use reference to "self" (which should be "cls" for classmethod).

[py3] Use six.text_type instead of unicode in _CWSourceCfgMixIn.update_config()

[server] Drop condition on "3.10" migration in repo.init_sources_from_database() We'll duplicate the code of this method in forthcoming changeset so clean it up a bit of old stuff.

[pkg] Version 3.25.0rc2

[doc] More release note about session data handling mentionning deprecation of _cw.data and removal of get/set_shared_data.

[session] Drop long deprecated [get/set]_shared_data methods they are deprecated since 3.19 and access to the .data attribute itself deprecated in 3.25, so it's time to drop them.

[session] Drop the user session synchronization machinery which should not be necessary anymore since groups and properties are fetched for each request (cache lives in transaction_data).

[session] Avoid deprecation warning on access to Connection.data this attribute has been deprecated during the session related rework, remove warning by explicitly storing data in .transaction_data since session data is not anymore reachable through Connection object. This will allows simplification of session synchronization hooks in a later cset. Also since we do not rely anymore on session data here, we may at some point rewrite those properties to rely on the ORM instead of such custom caching.

[doc] Add release note about change in uicfg