Keep knowledge of a ghost as long as possible
INSERT the ghost before we actually join them to the room. Only DELETE them
after we get the self-presence about them leaving.
Do not INSERT and join when we get presence errors or presence unavaiable!
If a ghost has leaked through, remove it
Allow specifying nickLength for a MUC
Custom tag per source and nick char filter for target
Detect ghost presence from DB instead of by looking for tag in nick
Remove stale nicks that are no longer present on other side after restart
Replace mentioned nicks with their ghost equivalent