- add python 3.6+ type hints
- replace applying defaults dict in LDAPSettings with actual variables, allowing type hints, checking if variable exists (e.g. IDE), and preventing supplied defaults dict (LDAPSettings.__init__) to inject undesired variables
- add AbstractLDAPSearch as abstract base class
- fix (by removing) result of search_s not being checked if None in LDAPSearch.execute
- add conversion to string in AbstractLDAPSearch._escape_filterargs
- rename AbstractLDAPSearch._begin(...) to AbstractLDAPSearch._search(...) and AbstractLDAPSearch._results(...) to AbstractLDAPSearch._result(...)
- add AbstractLDAPSearch._abandon(...)
- LDAPSearch._search(...) saves the msgid inside the object instead of returning it
- make LDAPGroupType abstract
- MemberDNGroupType.is_member(...) now returns bool instead of Union[bool, int]
- remove kwargs from LDAPGroupQuery.__init__
- update test mocks corresponding to the AbstractLDAPSearch changes

…to instance variables

- remove unused variables supports_anonymous_user, supports_object_permissions, and supports_inactive_user
- move settings_prefix to LDAPSettings
- remove default_settings
- change _settings and _ldap from class variables to instance variables
- add __setstate__ to set excluded properties to the object