Cleanup contact settings when the contact no longer exists

[diederik]

When a contact is removed in an other client, it's settings are still stored in the "kmessrc" file. After all contacts are received, KMess should cleanup stale entries in the settings file.

It's recommended to build a list of contacts to remove first, because this code likely needs to change when "contact list caching" is implemented (the MSN servers won't send all contact data anymore then).

[amroth]

It's one of the first patches I've written :P