backends. This is a port to master from PR #7745
remove OC_GROUP_BACKEND_GET_DISPLAYNAME option for group backends
Conflicts:
lib/private/group/backend.php
LDAP: getDisplayNamesInGroup is not an option for group backends anymore
Conflicts:
apps/user_ldap/group_ldap.php
apps/user_ldap/group_proxy.php
clean up group backends
Conflicts:
lib/private/group/database.php
remove now unnecessary test
implement getDisplayNames in group manager
adjust user manager tests
test for group manager's displayNamesInGroup
trim must not be used in empty in PHP < 5.5
keep the constant to not provoke PHP warnings
Conflicts:
lib/private/group/backend.php
