User Settings: Enable changes in external Ldap

[abarz722]

To make changes in external Ldap the write user has to be set in the connection. To enable the "resetPassword" or "Edit" button in the user settings, knowledge about the origin (Ldap) of the user has to be saved. So we need:

• new database field in uiusers table (e.g. origin-Ldap or just a writable-flag)
• logic to fill this field at user generation time (first login for external, create for internal users)
• logic to use it in user settings