v1.2.1: Added start with a ticket option

1. Added 'ALFRESCO_TICKET: with ALFRESCO_AUTH_METHOD=ticket, a login ticket you already hold is used as-is instead of being fetched from a username and password — so the server can run with no Alfresco password configured at all. Leave it unset and ticket auth behaves as before (acquired from ALFRESCO_USERNAME/ALFRESCO_PASSWORD`). A supplied ticket is never renewed, so it stops working when it expires.
2. Requires python-alfresco-api >= 1.2.2 for the ticket pass-through above.
3. Fixed Integration test test_search_shared_folder: now passes node_type="cm:folder". search_content searches documents (cm:content) by default, so the search never matched the Shared folder and the test failed.