Add function to ensure a handle by its name (create it if not found)
Add function to ensure a handle by its name (create it if not found)

Connection managers can't override create_handle and normalize_handle to have more specific behaviours. Extra arguments can be given to create handles.

freedesktop-unofficial-mirror/telepathy__telepathy-python,detrout/telepathy-python,max-posedon/telepathy-python,freedesktop-unofficial-mirror/telepathy__telepathy-python,detrout/telepathy-python,max-posedon/telepathy-python