Added possibility of displaying timestamp of starting being away state.

It is a nice feature for my friends to see in a simple way at what time I've last time been seen. This feature provides possibility of adding customized time-stamp of last seen time.

Example message: "All Quassel clients vanished from the face of the earth... %%hh:mm:ss%%" which formats to: "All Quassel clients vanished from the face of the earth... 23:20:34"